13.

PRACTICAL WORK

Intext Questions
Question 1
(a) Give only one suitable chemical test to identify the following gases.

(i) Ammonia

(ii) Sulphur dioxide

(iii) Hydrogen chloride

(iv) Chlorine

(v) Carbon dioxide

(vi) Oxygen

(vii) Hydrogen

(b) Select a basic gas mentioned in Q. 1(a). How is the basic nature suspected?

(c) Select acidic gases from the gases mentioned in Q. 1 (a). How is the acidic nature suspected?

(d) The two gases A and B are bleaching agents. A is greenish yellow and bleaches due to it's oxidising property while B
a colourless gas bleaches due to reduction. Identify A and B.

(e) Which gas turns blue cobalt chloride paper light pink?

Give one similarity in test between (i) Cl2 and HCl (ii) SO2 and CO2.

Answer

(i) Ammonia — When a glass rod dipped in conc. HCl is brought near the gas, dense white fumes of ammonium chloride
are formed.

(ii) Sulphur dioxide — Sulphur dioxide gas turns acidified potassium permanganate from pink to clear colourless and
acidified potassium dichromate from orange to clear green.

(iii) Hydrogen chloride — Forms a curdy white ppt. on passage through AgNO3 solution. The precipitate dissolves in
excess of NH4OH.

(iv) Chlorine — Chlorine turns moist blue litmus red and then bleaches it.

(v) Oxygen — Oxygen gas rekindles a glowing wooden splinter.

(iv) Hydrogen — Hydrogen gas burns with a 'pop' sound in air.

(b) Ammonia is a basic gas. It turns red litmus blue.

(c) Sulphur dioxide, Hydrogen chloride, Chlorine, Carbon dioxide.

(d) A is Chlorine and B is Sulphur dioxide.

(e) Water vapour

(i) Similarity in test of Cl2 and HCl — Forms a white ppt. on reaction with AgNO3 solution.

(ii) Similarity in test of SO2 and CO2 — Both turn lime water milky.

Question 2
Name the gases which

(a) extinguishes burning wooden splinter.

(b) turns moist red litmus blue.

(c) do no effect on moist litmus.

(d) affect the acidified K2Cr2O7 paper and also turns lime water dirty milky.

Answer

(a) NH3, HCl, SO2, H2S, CO2, NO2, Cl2.

(b) Ammonia [NH3]

(c) Water vapour, hydrogen, oxygen

(d) sulphur dioxide [SO2]

Question 3
Name:

(a) Two carbonates which do not produce carbon dioxide on heating.

(b) A colourless gas which bleaches

(c) Gases which have sour taste

(d) Greenish yellow gas which also bleaches

(e) Gas with rotten egg smell.

Answer

(a) Sodium carbonate [Na2CO3] and potassium carbonate [K2CO3]

(b) Sulphur dioxide [SO2]

(c) Carbon dioxide [CO2]

(d) Chlorine [Cl2]

(e) Hydrogen sulphide [H2S]

Exercise 13
Question 1
From the following list of substances choose those which meet the description given below.

1. Ammonium chloride
2. Ammonium nitrate
3. Chlorine
4. Dilute hydrochloric acid
5. Iron
6. Lead nitrate
7. Manganese (IV) oxide
8. Silver nitrate
9. Sodium nitrate
10. Sodium nitrite
11. Sulphur

Two compounds whose aqueous solutions give white precipitates with dilute hydrochloric acid.

Answer

Silver nitrate and Lead nitrate.

HCl + AgNO3 ⟶ AgCl + HNO3

2HCl + Pb(NO3)2 ⟶ PbCl2 + 2HNO3

Question 2

Name the anion present in each of the following compounds.

(a) Compound A when warmed with concentrated sulphuric acid gives a gas which fumes in moist air and which gives
dense white fumes with ammonia.
(b) When barium chloride solution is added to a solution of compound B, a white precipitate insoluble in dilute
hydrochloric acid is formed.

(c) The action of heat on the insoluble compound C produces a gas which turns lime water turbid.

(d) Compound D when warmed with dilute sulphuric acid gives a gas which turns acidified dichromate solution green.

Answer

(a) Cl-

(b) SO42-

(c) CO32-

(d) SO32-

Question 3
A given white crystalline salt was tested as follows :

(a) It dissolved in water and the resulting solution of the salt turned blue litmus red.

(b) Addition of barium chloride solution into this solution gave a white precipitate.

(c) A flame test on the salt gave a persistent golden-yellow colourisation.

What conclusion can be drawn for each observation?

Answer

(a) As the salt solution turned blue litmus red hence the salt may be an acid.

(b) As white ppt. is obtained on addition of barium chloride so the salt may contain SO42-, SO32-, CO32-.

(c) Persistent golden yellow colourisation which suggests presence of Na+ ion.

Question 4
(a) Sodium hydroxide solution is added to solution A. A white precipitate is formed which is insoluble in excess sodium
hydroxide solution. Name the metal ion present in solution A.

(b) When ammonium hydroxide is added to solution B, a pale blue precipitate is formed. This pale blue precipitate
dissolves in excess ammonium hydroxide giving an inky blue solution. Name the cation present in solution B.

(c) When an ammonium salt is warmed with sodium hydroxide solution, ammonia gas is evolved. State three ways in
which you could identify this gas.

Answer

(a) Ca2+

(b) Cu+

(c) The three ways to identify ammonia gas are:

1. Ammonia gas turns moist red litmus turns blue.

2. If a glass rod dipped in concentrated HCl is brought near the gas, dense white fumes of ammonium chloride
are formed.
3. The gas turns colourless Nessler's reagent i.e. K2HgI4 potassium mercuric iodide brown.

Question 5
Complete the following table and write your observations.

Hydrogen Sulphur Hydrogen

Ammonia
sulphide dioxide chloride

Shake the gas with red

litmus solution
 Hydrogen Sulphur Hydrogen
Ammonia
sulphide dioxide chloride

Shake the gas with blue

litmus solution

Apply a burning splint to the

gas

Answer

Hydrogen Hydrogen
Ammonia Sulphur dioxide
sulphide chloride

Shake the gas

Red litmus
with red litmus No change No change No change
becomes blue
solution

Shake the gas

Blue litmus Blue litmus Blue litmus
with blue No change
becomes red becomes red becomes red
litmus solution

Apply a
Burning splint is Burning splint is Burning splint is Burning splint is
burning splint
extinguished extinguished extinguished extinguished
to the gas

Question 6
Use the information given in (a) to (h) to identify the substances P to W selecting your answers from the given list.

List

Calcium Oxygen Copper (II) oxide

Carbon Calcium hydroxide Copper (II) nitrate

Lead (II) oxide Hydrogen chloride Chlorine

Lead (II) nitrate Calcium oxide Ammonium chloride

(a) P is a white solid. When heated produces white fumes (sublime).

(b) P and R on warming produce an alkaline gas.

(c) On adding water to T, heat is evolved and R is formed.

(d) Q burns brightly in air to form T.

(e) When S is heated, it gives off brown fumes and leaves a black residue of U.

(f) A solution of S is formed by warming U with dilute nitric acid.

(g) V is a gaseous non-metallic element that reacts with hydrogen to form W.

(h) A solution of W will neutralise the solution of R.

Answer

(P) Ammonium chloride

(Q) Calcium

(R) Calcium hydroxide

(S) Lead (II) Nitrate

(T) Calcium Oxide

(U) Lead (II) Oxide

(V) Chlorine

(W) Hydrogen chloride

Question 7
Copy and complete the following table which refers to the action of heat on some carbonates :

Carbonate Colour of residue on cooling

Zinc carbonate

Lead carbonate

Copper carbonate

Answer

Carbonate Colour of residue on cooling

Zinc carbonate White

Lead carbonate Yellow

Copper carbonate Black

Question 8
Distinguish by a chemical test :

(a) Sodium carbonate and sodium sulphite

(b) Sodium chloride and sodium sulphide

(c) Sodium hydroxide solution and ammonium hydroxide solution.

(d) Ammonium sulphate and sodium sulphate.

(e) Sulphuric acid from nitric acid and hydrochloric acid.

Answer

(a) When dil. sulphuric acid is added to sodium carbonate and heated, colourless, odourless gas is evolved which turns
lime water milky and has no effect on KMnO4 or K2Cr2O7 solutions.

When dil. sulphuric acid is added to sodium sulphite and heated, colourless gas with suffocating odour is evolved which
turns lime water milky. It turns acidified K2Cr2O7 from orange to clear green and pink coloured KMnO4 to clear colourless.

Hence, the two compounds can be distinguished.

(b) When dil. sulphuric acid is added to sodium sulphide and heated, hydrogen sulphide gas is evolved which has the
smell of rotten eggs and turns lead acetate paper black.
Whereas, when conc. sulphuric acid is added to sodium chloride and heated, HCl gas is evolved which gives dense white
fumes when a glass rod dipped in ammonia is brought near it.

(c) When ammonium hydroxide is reacted with a solution of copper sulphate, a pale blue ppt. of copper hydroxide is
formed which dissolves in excess of ammonium hydroxide forming a deep blue solution of a soluble complex salt
[Cu(NH3)4]SO4 [tetramine copper [II] sulphate] .

CuSO4 + 2NH4OH ⟶ (NH4)2SO4 + Cu(OH)2 ↓

Cu(OH)2 + (NH4)2SO4 + 2NH4OH ⟶ [Cu(NH3)4]SO4 + 4H2O

Whereas, when copper sulphate is added to sodium hydroxide solution, pale blue ppt. of copper hydroxide is obtained
which is insoluble in excess of sodium hydroxide.

CuSO4 + 2NaOH ⟶ Na2SO4 + Cu(OH)2 ↓

(d) When ammonium sulphate is heated with NaOH, ammonia gas is produced which turns red litmus blue whereas,
sodium sulphate does not react with sodium hydroxide.

(NH4)2SO4 + 2NaOH ⟶ Na2SO4 + 2H2O + 2NH3

Na2SO4 + NaOH ⟶ no reaction.

(e) Barium chloride reacts with dil H2SO4 to form a white ppt. of barium sulphate.

BaCl2 + H2SO4 [dil.] ⟶ 2HCl + BaSO4 ↓ [white ppt.]

Whereas, HCl and nitric acid does not form a white ppt.

BaCl2 + HCl ⟶ No white ppt.

BaCl2 + HNO3 ⟶ No white ppt

Question 9
Sodium hydroxide solution is added first in a small quantity, then in excess to the aqueous salt solutions of copper (II)
sulphate, zinc nitrate, lead nitrate, calcium chloride and iron (III) sulphate. Copy the following table and write the colour of
the precipitate in (i) to (v) and the nature of the precipitate (soluble or insoluble) in (vi) to (x).

Nature of precipitate (soluble or

Aqueous salt Colour of precipitate when NaOH
insoluble) when NaOH is added in
solution is added in a small quantity
excess

Copper (II)
(i) (vi)
sulphate

Zinc nitrate (ii) (vii)

Lead nitrate (iii) (viii)

Calcium
(iv) (ix)
chloride

Iron (III)
(v) (x)
sulphate

Answer
 Nature of precipitate (soluble or
Aqueous salt Colour of precipitate when NaOH
insoluble) when NaOH is added in
solution is added in a small quantity
excess

Copper (II)
(i) Pale blue (vi) Insoluble
sulphate

Zinc nitrate (ii) White gelatinous (vii) Soluble

Lead nitrate (iii) White chalky (viii) Soluble

Calcium
(iv) White curdy (ix) Insoluble
chloride

Iron (III)
(v) Reddish brown (x) Insoluble
sulphate

Question 10
State your observations when:

(a) lead nitrate solution and sodium chloride solution are mixed.

(b) zinc chloride solution, zinc nitrate solution and zinc sulphate solutions are added individually to

(i) barium chloride solution,

(ii) lead nitrate solution.

(c) Decomposition of bicarbonates by dil. H2SO4

2NaHCO3 + H2SO4 ⟶ Na2SO4 + 2H2O + 2CO2

2KHCO3 + H2SO4 ⟶ K2SO4 + 2H2O + 2CO2

Answer

(a) When lead nitrate solution is mixed with sodium chloride solution, a white precipitate of lead chloride is seen and the
soluble salt sodium nitrate is formed.

2NaCl + Pb(NO3)2 ⟶ 2Na(NO3)2 + PbCl2↓

Precipitate of lead chloride and sodium nitrate are formed.

(b)

Zinc Chloride Zinc Nitrate

Zinc Sulphate Solution
Solution Solution

Barium Chloride No ppt. White ppt. is obtained which is

No reaction
Solution observed insoluble in mineral acid.

Lead Nitrate White ppt. is

No reaction No ppt. observed
Solution obtained

(c) Carbon dioxide gas is evolved with brisk effervescence which turns blue litmus red and extinguishes a burning
wooden splinter.
Question 11
The questions (i) to (v) refer to the following salt solutions listed A to F.

A. Copper nitrate

B. Iron (II) sulphate

C. Iron (III) chloride

D. Lead nitrate

E. Magnesium sulphate

F. Zinc chloride

(i) Which two solutions will give a white precipitate when treated with dilute hydrochloric acid followed by barium chloride
solution?

(ii) Which two solutions will give a white precipitate when treated with dilute nitric acid followed by silver nitrate solution?

(iii) Which solution will give a white precipitate, when either dilute hydrochloric acid or dilute sulphuric acid is added to it?

(iv) Which solution becomes a deep/inky blue colour when excess of ammonium hydroxide is added to it?

(v) Which solution gives a white precipitate with excess ammonium hydroxide solution?

Answer

(i) Iron (II) Sulphate and Magnesium sulphate

(ii) Iron (III) chloride and Zinc Chloride

(iii) Lead nitrate

(iv) Copper nitrate.

(v) Lead nitrate.

Question 12
Mention the colour change when following indicators are added:

Solution Acids Alkalies

(a) Alkaline phenolphthalein solution,

(b) Methyl orange solution,

(c) Neutral litmus solution

Answer

Solution Acids Alkalies

(a) Alkaline phenolphthalein solution, Colourless Pink

(b) Methyl orange solution Pink Yellow

(c) Neutral litmus solution Red Blue

Question 13
Salts A, B, C, D and E undergo reactions (i) to (v) respectively. Identify the anion present in these salts on the basis of
these reactions.

(a) When silver nitrate solution is added to a solution of A, a white precipitate, insoluble in dilute nitric acid, is formed.

(b) Addition of dilute hydrochloric acid to B produces a gas which turns lead acetate paper black.

(c) When a freshly prepared solution of ferrous sulphate is added to a solution of C and concentrated sulphuric acid is
gently poured from the side of the test-tube, a brown ring is formed.

(d) When dilute sulphuric acid is added to D, a gas is produced which turns acidified potassium dichromate solution from
orange to green.

(e) Addition of dilute hydrochloric acid to E produces an effervescence. The gas produced turns lime water milky but does
not affect acidified potassium dichromate solution.

Answer

(a) Chloride ion (Cl-)

(b) Sulphide ion (S2-)

(c) Nitrate (NO3-)

(d) Sulphite ion (SO32-)

(e) Carbonate ion (CO32-)

Question 14
(a) The salt which in solution gives a pale green precipitate with sodium hydroxide solution and a white precipitate with
barium chloride solution is :

(i) Iron (III) sulphate

(ii) Iron (II) sulphate

(iii) Iron (II) chloride

(iv) Iron (III) chloride

(b) Identify the following substances :

(i) An alkaline gas A which gives dense white fumes with hydrogen chloride.

(ii) Gas C has an offensive smell like rotten eggs.

(iii) Gas D is a colourless gas which can be used as a bleaching agent.

Answer

(a) Iron (II) sulphate

(b) A → Ammonia
C → Hydrogen sulphide
D → Sulphur dioxide

Question 1a(2009)
Carbon dioxide and sulphur dioxide gas can be distinguished by using

(i) moist blue litmus paper

(ii) lime water

(iii) acidified potassium dichromate paper

(iv) none of the above.

Answer

acidified K2Cr2O7 (potassium dichromate) paper

Reason

There is no effect of CO2 gas on potassium dichromate whereas SO2 turns acidified potassium dichromate from orange to
clear green.
K2Cr2O7 + H2SO4 + 3SO2 ⟶ K2SO4 + Cr2(SO4)3 + H2O

Question 1b(2009)
Identify the substance 'R' based on the information given below :

The pale green solid 'R' turns reddish brown on heating. Its aqueous solution gives a white precipitate with barium
chloride solution. The precipitate is insoluble in mineral acids.

Answer

The substance 'R' is Ferrous sulphate (FeSO4.7H2O).

Reason

When heated strongly, the hydrous pale green ferrous sulphate (FeSO4.7H2O), loses it's water of crystallization and
decomposes to form brown ferric oxide Fe2O3 along with sulphur dioxide (SO2) and sulphur trioxide (SO3).

FeSO4.7H2O →(Δ) FeSO4 + 7H2O

2FeSO4 →(Δ)Fe2O3 + SO2 + SO3

Ferrous sulphate on reaction with barium chloride soln., forms a white ppt. of barium sulphate (BaSO4) which is insoluble
in mineral acids.

Question 1c(2009)
Give one chemical test to distinguish between the following pairs of compounds.

(i) Zinc sulphate solution and zinc chloride solution

(ii) Iron (II) chloride soln. and iron (III) chloride soln.

(iii) Calcium nitrate soln. and calcium chloride soln.

Answer

(i) When BaCl2 soln. is added to ZnSO4, a white ppt. of BaSO4 is formed, whereas, no ppt. is formed in case of ZnCl2.
Hence, the two solns. can be distinguished.

BaCl2 + ZnSO4 ⟶ BaSO4 ↓ [white ppt.] + ZnCl2

BaCl2 + ZnCl2 ⟶ No white ppt.

(ii) When NaOH soln. is added to the given solns., FeCl2 reacts to form a dirty green ppt. of Fe(OH)2 whereas,
FeCl3 reacts to form a reddish brown ppt. of Fe(OH)3.

(iii) Add silver nitrate soln. to the given solns., calcium chloride reacts to form a white ppt. which is soluble in NH4OH and
insoluble in dil. HNO3. The other soln. is calcium nitrate.

CaCl2 + 2AgNO3 ⟶ 2AgCl ↓ [white ppt.] + Ca(NO3)2

Ca(NO3)2 + AgNO3 ⟶ no white ppt.

Question 1a(2010)
(a) Select the correct answer from A, B, C and D.

A. Nitroso iron (II) sulphate

B. Iron (III) chloride

C. Chromium sulphate

D. Lead (II) chloride.

(i) The compound which is responsible for the green colour formed when SO2 is bubbled through acidified potassium
dichromate solution.

(ii) Compound responsible for brown ring.

Answer

(i) Chromium sulphate

K2Cr2O7 + H2SO4 + 3SO2 ⟶ K2SO4 + Cr2(SO4)3 + H2O

(ii) Nitroso iron (II) sulphate

Question 1b(2010)
State your observation :

(i) a piece of moist blue litmus paper (ii) paper soaked in potassium permanganate solution — is introduced in each case
into ajar of sulphur dioxide.

Answer

(i) Moist blue litmus turns red.

(ii) Sulphur dioxide turns potassium permanganate from pink to clear colourless.

2KMnO4 + 2H2O + 5SO2 ⟶ K2SO4 + 2MnSO4 + 2H2SO4

Question 1c(2010)
Write the equation for the reaction of magnesium sulphate solution with barium chloride solution.

Answer

MgSO4 + BaCl2 ⟶ BaSO4 ↓ [white ppt.] + MgCl2

Question 1a(2011)
Choose from the list of substances — Acetylene gas, aqua fortis, coke, brass, barium chloride, bronze, platinum.

An aqueous salt solution used for testing sulphate radical.

Answer

Barium chloride.

Question 1a(2012)
Name — the gas which turns acidified potassium dichromate solution green.

Answer

Sulphur dioxide gas (SO2)

Question 1b(2012)
Identify the anion present in the following compounds :

(i) Compound X on heating with copper turnings and conc. sulphuric acid liberates a reddish brown gas.

(ii) When a solution of compound Y is treated with silver nitrate solution a white precipitate is obtained which is soluble in
excess of ammonium hydroxide solution.

(iii) Compound Z which on reacting with dilute sulphuric acid liberates a gas which turns lime water milky, but the gas has
no effect on acidified potassium dichromate solution.

(iv) Compound L on reacting with barium chloride solution gives a white precipitate insoluble in dilute hydrochloric acid or
dilute nitric acid.

Answer

(i) Nitrate ion, NO3-

(ii) Chloride ion, Cl-

(iii) Carbonate ion, CO32-

(iv) Sulphate ion, SO42-

Question 1c(2012)
State one chemical test between each of the following pairs :

(i) Sodium carbonate and sodium sulphite.

(ii) Ferrous nitrate and lead nitrate.

(iii) Manganese dioxide and copper (Il) oxide.

Answer

(i) When dil. sulphuric acid is added to sodium carbonate and heated, colourless, odourless gas is evolved which turns
lime water milky and has no effect on KMnO4 or K2Cr2O7 solutions.

When dil. sulphuric acid is added to sodium sulphite and heated, colourless gas with suffocating odour is evolved which
turns lime water milky. It turns acidified K2Cr2O7 from orange to clear green and pink coloured KMnO4 to clear colourless.

Hence, the two compounds can be distinguished.

(ii) When NaOH is added to each of the compounds, a dirty green precipitate of Iron [II] hydroxide [Fe(OH)2] is formed in
case of Ferrous nitrate whereas a chalky white precipitate of lead hydroxide [Pb(OH)2] is formed in case of lead nitrate.
Iron [II] Hydroxide [Fe(OH)2] is insoluble in excess of NaOH, whereas Lead Hydroxide [Pb(OH)2] is soluble in excess of
NaOH. Hence, the two compounds can be distinguished.

(iii) When each of the compound is heated with conc. hydrochloric acid, greenish yellow (chlorine) gas is evolved in case
of manganese dioxide and filtrate is brownish in colour whereas, no chlorine gas is evolved in case of copper (II) oxide
and filtrate is bluish in colour.

MnO2 + 4HCl ⟶ MnCl2 + 2H2O + Cl2

CuO + 2HCl ⟶ CuCl2 + H2O

Question 1a(2013)
Give a chemical test to distinguish between :

(i) Sodium chloride soln. and sodium nitrate soln.

(ii) Hydrogen chloride gas and hydrogen sulphide gas.

(iii) Calcium nitrate soln. and zinc nitrate soln.

(iv) Carbon dioxide gas and sulphur dioxide gas.

Answer

(i) Add silver nitrate soln. to the given solns., sodium chloride reacts to form a white ppt. which is soluble in NH4OH and
insoluble in dil. HNO3. The other soln. is sodium nitrate.

NaCl + AgNO3 ⟶ AgCl ↓ [white ppt.] + NaNO3

NaNO3 + AgNO3 ⟶ no white ppt.

(ii) Hydrogen sulphide gas turns moist lead acetate paper silvery black or black whereas, no change is observed in case
of HCl gas.

Pb(CH3COO)2 [colourless] + H2S ⟶ PbS [black] + 2CH3COOH

(iii) When NaOH is added to the given soln., Zn(NO3)2 reacts to form a gelatinous white ppt. which dissolves in excess of
NaOH whereas, Ca(NO3)2 forms a milky white ppt. which is insoluble in excess of NaOH. Hence, the two can be
distinguished.

(iv) Carbon dioxide gas has no effect on acidified potassium permanganate (KMnO4) and acidified potassium dichromate
(K2Cr2O7) solution whereas sulphur dioxide gas turns acidified potassium permanganate from pink to clear colourless and
acidified potassium dichromate from orange to clear green.

2KMnO4 + 2H2O + 5SO2 ⟶ K2SO4 + 2MnSO4 + 2H2SO4

K2Cr2O7 + H2SO4 + 3SO2 ⟶ K2SO4 + Cr2(SO4)3 + H2O

Question 1a(2014)
Distinguish between : Sodium nitrate and sodium sulphite [using dilute sulphuric acid].

Answer

Sodium nitrate will not react with dilute sulphuric acid.

Sodium sulphite reacts with dil. sulphuric acid and colourless gas with suffocating odour is evolved which turns lime water
milky.

Question 1b(2014)
State your observation : When moist starch iodide paper is introduced into chlorine gas.

Answer

Chlorine gas turns moist starch iodide paper blue black.

Cl2 + 2KI ⟶ 2KCl + I2

[Starch + I2 ⟶ blue black colour]

Question 1c(2014)
The flame test with a salt P gave a brick red flame. What is the cation in P.

Answer

Cation in P is Ca2+ (calcium ion).

Question 1d(2014)
A gas Q turns moist lead acetate paper silvery black. Identify the gas Q.

Answer

The gas Q is H2S (Hydrogen sulphide).

Pb(CH3COO)2 [colourless] + H2S ⟶ PbS [black] + 2CH3COOH

Question 1e(2014)
pH of liquid R is 10. What kind of substance is R ?

Answer

R is an alkaline substance.