Which molecule has ionic bond?
Mg
C0
NaCl
N0

Explanation:

Concentration of benzoic acid, [benzoic acid] =1M (initially)

concentration of benzoate, [benzoate] =1M (initially)

Let's consider V ml of benzoic acid be taken.

So (300−V) ml of sodium benzoate is taken.

∴ [benzoicacid]

final

=

300ml

1M×Vml

[benzoate]

final

=

300ml

1M×(300−V)ml

∴ pH=pK

a

+log

[benzoicacid]

final

[benzoate]

final

⇒4.5=4.2+log{

V/300

(300−V)/300

}

⇒

V

300−V

=10

0.3

≈2

⇒V=100ml

∴ 100ml of benzoic acid had been taken.