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Mass number of helium=4
1 mole of helium gas is present in 4 g of helium gas
1 gm of helium gas contains 1÷4 moles of helium
0.49gm contains 0.49÷4 moles of helium
=0.1225 moles
The formula for calculating number of moles is as follows:
no.moles= mass/molar mass
mass of helium is 0.49 g
molar mass of helium is 4 g/mol
moles of He= 0.49g/4g/mol
=0.1225 mol.
Therefore, the no.of moles of helium is 0.1225 mol