Answer:

Explanation:
We will need a chemical equation with masses and molar masses, so, let's gather all the information in one place.
Mᵣ: 28.01 17.03
N₂ + 3H₂ ⟶ 2NH₃
m/g: 240.0
(a) Moles of NH₃

(b) Moles of N₂

(c) Mass of N₂

Answer:

Explanation:
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In this case, according to the given information it turns out possible for us to realize that one mole of the given compound, Mg(ClO₄)₂, has one mole of Mg, two moles of Cl and eight moles of O; thus, we proceed as follows:

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4% mass / volume :
4 g ---------> 100 mL
1.2 g ------- ? mL
V = 1.2 * 100 / 4
V = 120 / 4
V = 30 mL
hope this helps!