KCET 2021 Chemistry Solved Paper

Ethyne on reaction with HgSO4∕H2SO4 gives ethanol (i.e. CH2=CH−OH) which interconvert (i.e. tautomerises) to give acetaldehyde (CH3‌CHO).
PCC is an oxidising agent, which oxidised the alcohol to aldehyde. Therefore, (B) is an alcohol, i.e. ethanol.
CH3CH2‌OH‌

PCC

────▶

‌CH3‌CHO
Ethane nitrile on reaction with SnCl2∕HCl followed by acid hydrolysis give acetaldehyde.
CH3‌CN‌

(i)SnCl2∕HCl

─────▶

(ii)H3O+

‌CH3‌CHO