What is the total number of electrons present in 16 grams of methane gas?

1 molecule of CH4 has 6+4(1)=10 electrons

Avagadro number is equal to one mole

So,

One mole of CH4 has 10*avagadro numbers of electrons

1 mole of methane gas weighs 12+4(1)=16g

Therefore,

16 grams of CH4 contain 10*6.023*1023 electrons = 6.623*1024 electrons.