Question

Degree of ionisation of 1 M HCOOH is decreased to a maximum extent in presence of:
(A) 1 M HCHO
(B) 1 M NaOH
(C) 1 MHCOONa
(D) equally in all

Answer 1

hcooh is acid and naoh is base.
answer is b

Answer 2

(C) HCOO Na

H COOH is formic acid which is a weak acid.  H CHO is  Formaldehyde or Methanal.  It is very weak acid or we can say it does not decompose at all.  So Formaldehyd does not affect decomposition of Formic acid.

Na OH is a strong base.  It decomposes fully.  So OH⁻ ions will attract H⁺ from Formic acid.

 HCOONa is a Sodium salt (Sodium Formate). It decomposes in solution. It gives COOH⁻ ions.  So this hinders Formic acid from dissociating into ions: COOH⁻ and H⁺ .