The question is Incomplete.
How many oxygen atoms are in 0.25 mol calcium nitrate?
Answer:-
9.0345 x 10^23
Explanation:-
The chemical formula for Calcium Nitrate is Ca(NO3)2
From the formula we find there are a total of 3 x 2 = 6 Oxygen O atoms in 1 molecule of Calcium nitrate.
We know from Avogadro's Law that 1 mol of a compound has 6.023 x 10^ 23 molecules.
Number of moles of calcium nitrate = 0.25
Number of molecules of Ca(NO3)2 = 0.25 x 6.023 x 10^23
= 1.5075 x 10^23
Number of atoms of O = 6 x 1.5075 x 10^23
= 9.0345 x 10^23