Question

atomic no. of oxygen is 6 or 12?? in periodic table it is 6 but in topic 2 of mritnation it is given 12

Answer 1

I think 12 is atomic number of oxygen.

Answer 2

Dear mate,

Atomic number of oxygen is 6, that is because of 6 protons.
Atomic mass is 12, as its nucleus comprises 6 protons and 6 neutrons.

It does not matter, what is mentioned in any particular website. Just ignore that.

Hope it helps.