Calculate the mols for 4.2g of a Mg
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0.175mol

Explanation:

Mole of a substance can be calculated using the formula as follows:

number of moles (n) = mass (m) ÷ molar mass (MM)

According to this question, there are 4.2g of Magnesium (Mg).

Molar mass of Magnesium = 24g/mol, hence, the number of moles of 4.2g of Mg is as follows:

n = 4.2g ÷ 24g/mol

n = 0.175mol

i believe it is c.) 1575 j.