Equal volumes of 0.1 M AgNO3 and 0.2 M NaCl are mixed. The concentration of NO3-ion in the mixture will be:

When equal volumes  of solution are mixed then total  volume will be doubled.

As volume is inversely proportional to concentration.

Hence concentration will be half of initial concentration.

The concentration of NO3- ions in the mixture will be halved .

Concentration  of NO3- ion = 0.12 = 0.05

Hence the correct answer is (B) 0.05 M