The molecular weights of the given elements are as follows:
He = 4, Na = 23, Ca = 40.
To check which element has most atoms, we need to check the number of moles present in each option. The highest number of moles mean the most atoms present.
No. of moles = Given weight/molecular weight of the element
For 4g He, no. of moles are 4/4 = 1 mol.
For 46g Na, no. of moles are 46/23 = 2 mol.
For 0.40g Ca, no. of moles are 0.4/40 = 0.01 mol.
For 12g He, no. of moles are 12/4 = 3 mol.
Therefore, 12g He contains the most number of atoms.
The correct answer is (iv).
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