Cell volume mainly depend on (a)Naand K cotransport(b)Na K influx (c)NaAnd k out flux

Dear Student, 
The correct option is option A i.e. sodium potassium co transport.
At resting stage of a neuron:

Axonal membrane is more permeable to K⁺ and nearly impermeable to Na⁺.It is impermeable to negatively charged proteins present inside the axoplasm. Thus, it does not let them go out.

As a result, the axoplasm has more concentration of K⁺ and negatively charged proteins, and less concentration of Na⁺. This creates a concentration gradient.

Gradient is maintained by the Sodium-Potassium Pump which pumps 3 Na⁺ out and 2 K⁺ in.

Regards