Chem MC

1. The answer should be C. (1), (3).

For (1). Chlorine is yellowish-green in colour. Bromine is orange-red. Iodine is black. So the colour of these three elements gets darker down the periodic table. So, this statement is correct.

For (2). The reactivity for the elements in group 7 decreases down the group. In other words, their reactivity should decreases with increasing relative atomic mass. So this statement is wrong.

For (3). They all react with sodium sulphite solution as shown below. Take chlorine as an example.

SO3 2- (aq) + H2O (l) → 2H+ (aq) + SO4 2- (aq) + 2e-
Cl2 (g) + 2e- → 2Cl- (aq)
───────────────────────────────────
Cl2 (g) + SO3 2- (aq) + H2O (l) → 2H+ (aq) + SO4 2- (aq) + 2Cl- (aq)



For you to determine whether a chemical is an oxidizing agent or reducing agent, you have to look of the other chemicals.

So, for chloride ion to be a reducing agent, the other chemical should be an oxidizing agent like sulphate ion.

4H+ (aq) + SO4 2- (aq) + 2e- → SO2 (g) + 2H2O (l)
2Cl- (aq) → Cl2 (g) + 2e-
─────────────────────────────────────────
2Cl- (aq) + 4H+ (aq) + SO4 2- (aq) → Cl2 (g) + SO2 (g) + 2H2O (l)


By the same principle, for iodine to be an oxidzing agent, a reducing agent should be used. Such as Iron (II) nitrate.

Fe2+ (aq) → Fe3+ (aq) + e-
I2 (aq) + 2e- → 2I- (aq)
─────────────────────────────────────────
2Fe2+ (aq) + I2 (aq) → 2Fe3+ (aq) + 2I- (aq)