For making a capacitor, it is better to select a dielectric having

Option A: low permittivity

A dielectric with low permittivity would result in a capacitor with lower capacitance. This is not desirable for most applications where higher capacitance is needed.

Option B: high permittivity

A dielectric with high permittivity increases the capacitance of a capacitor. Higher permittivity means the dielectric material can store more electric energy for the same electric field, making it a better choice for capacitors.

Option C: permittivity same as that of air

Using a dielectric with the same permittivity as air would not provide any advantage over using air itself. It would not enhance the capacitance of the capacitor significantly.

Option D: permittivity slightly more than that of air

While a dielectric with permittivity slightly more than that of air would increase the capacitance somewhat, it would not be as effective as a dielectric with high permittivity.

Conclusion:

To make a capacitor with higher capacitance, it is better to select a dielectric with high permittivity, making Option B the correct answer.