Question detail

What is the number of moles in 100 grams of magnesium oxide (MgO)?

Try the question, check the answer, then read the explanation to understand the curriculum point.

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At a glance

MCQ

Type

practice

Style

Topic

Use of amount of substance in relation to masses of pure substances

Question

A. 1.25 mol
B. 0.5 mol
C. 2 mol
D. 3 mol

Answer

1.25 mol

Explanation

The relative formula mass of magnesium oxide (MgO) is 40 g/mol (Mg) + 16 g/mol (O) = 56 g/mol. Therefore, 100 g of MgO corresponds to 100 g / 56 g/mol = 1.25 moles.

Common mistake

Confusing Mass and Moles

Students often confuse mass (in grams) with the number of moles when calculating the amount of substance.

Always remember to use the formula: moles = mass / relative formula mass, ensuring you convert mass to the correct unit before calculation.

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