The number of collison is independent of volume
In 1 mole of magnesium there are Avogadro's number of atoms are present.
Avogadro's number = 6.023 x 10²³
1 mole = 6.023 x 10²³ atoms
3.75 moles = 3.75 x 6.023 x 10²³
=2.26 x 10²⁴
So, in 3.75 moles of magnesium there are 2.26 x 10²⁴ atoms of magnesium are present.
So, the answer would be 20 cm
25% of 20
%=100
25/100 x 20
1/4 x 20
The answer is equal to 5