${\mathrm{CH}}_3\mathrm{COOAg}+{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{Cl}⟶\mathrm{A}$. Wrong statement about ‘A’ is

${\mathrm{CH}}_3\mathrm{COOAg}+{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{Cl}\to \underset{\mathrm{A}}{{\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5}+\mathrm{AgCl}$

So, A is an ester.
IUPAC name of ‘A’ is ethyl ethanoate.
Butyric acid is ${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{COOH}$ . So, both compound ‘A’ and butyric acid have a molecular formula of ${\mathrm{C}}_4{\mathrm{H}}_8{\mathrm{O}}_2$.
Thus, both of them are functional isomers.
${\mathrm{CH}}_3{\mathrm{CH}}_2-$group in ‘A’ has ${\mathrm{sp}}^3$hybridized carbon atoms.
Hence, fourth option is incorrect.