Chemistry - Complete P-block Question with Solution | TestHub

The question asks to identify the number of reactions that produce SO₂ and involve an increase in the oxidation number of the underlined atom. This implies the underlined atom is oxidized, and concentrated H₂SO₄ acts as an oxidizing agent, getting reduced to SO₂.

Let's analyze each reaction:

(i) $\underline{\mathrm{Cu}}+{\mathrm{H}}_2{\mathrm{SO}}_4$ (conc.)

Reaction: $\underline{\mathrm{Cu}}+2{\mathrm{H}}_2{\mathrm{SO}}_4(conc.)\to {\mathrm{CuSO}}_4+{\mathrm{SO}}_2+2{\mathrm{H}}_2\mathrm{O}$

Oxidation state of Cu: $0\to +2$ (increases)

SO₂ is produced.

This reaction satisfies the conditions.

(ii) $\mathrm{HBr}+{\mathrm{H}}_2{\mathrm{SO}}_4$ (conc.)

Reaction: $2\mathrm{HBr}+{\mathrm{H}}_2{\mathrm{SO}}_4(conc.)\to {\mathrm{Br}}_2+{\mathrm{SO}}_2+2{\mathrm{H}}_2\mathrm{O}$

Oxidation state of Br in HBr: $-1\to 0$ in Br₂ (increases)

SO₂ is produced.

This reaction satisfies the conditions.

(iii) $\underline{\mathrm{S}}+{\mathrm{H}}_2{\mathrm{SO}}_4$ (conc.)

Reaction: $\underline{\mathrm{S}}+2{\mathrm{H}}_2{\mathrm{SO}}_4(conc.)\to 3{\mathrm{SO}}_2+2{\mathrm{H}}_2\mathrm{O}$

Oxidation state of S: $0\to +4$ in SO₂ (increases)

SO₂ is produced.

This reaction satisfies the conditions.

(iv) $\underline{\mathrm{C}}+{\mathrm{H}}_2{\mathrm{SO}}_4$ (conc.)

Reaction: $\underline{\mathrm{C}}+2{\mathrm{H}}_2{\mathrm{SO}}_4(conc.)\to {\mathrm{CO}}_2+2{\mathrm{SO}}_2+2{\mathrm{H}}_2\mathrm{O}$

Oxidation state of C: $0\to +4$ in CO₂ (increases)

SO₂ is produced.

This reaction satisfies the conditions.

(v) $\underline{\mathrm{P}}+{\mathrm{H}}_2{\mathrm{SO}}_4$ (conc.)

Reaction: $2\underline{\mathrm{P}}+5{\mathrm{H}}_2{\mathrm{SO}}_4(conc.)\to 2{\mathrm{H}}_3{\mathrm{PO}}_4+5{\mathrm{SO}}_2+2{\mathrm{H}}_2\mathrm{O}$

Oxidation state of P: $0\to +5$ in H₃PO₄ (increases)

SO₂ is produced.

This reaction satisfies the conditions.

(vi) ${\mathrm{Fe}}^{+3}+{\mathrm{H}}_2{\mathrm{SO}}_4$ (conc.)

Fe³⁺ is already in a high oxidation state and is not easily oxidized further by H₂SO₄. No SO₂ is produced.

This reaction does not satisfy the conditions.

(vii) $\mathrm{NaCl}+{\mathrm{H}}_2{\mathrm{SO}}_4$ (conc.)

Reaction: $\mathrm{NaCl}+{\mathrm{H}}_2{\mathrm{SO}}_4(conc.)\to {\mathrm{NaHSO}}_4+\mathrm{HCl}$

This is an acid-base reaction, not a redox reaction where SO₂ is produced.

This reaction does not satisfy the conditions.

Reactions (i), (ii), (iii), (iv), and (v) produce SO₂ and involve an increase in the oxidation number of the underlined atom.

Therefore, there are 5 such reactions.

The final answer is $\boxed{5}$.