Answer:
B) 12.9 grams.
Explanation:
How many moles of molecules in that 6.30 L of H₂?
The volume of one mole of an ideal gas at STP (0 °C, 1 atm) is 22.4 liters.
(The volume of that one mole of gas at STP will be 22.7 liters if STP is defined as 0 °C and 10⁵ Pa).
.
How many moles of Na will be needed?
The coefficient in front of Na in the equation is twice the coefficient in front of H₂. It takes two moles of Na to produce one mole of H₂.
.
What's the mass of that many Na atoms?
Refer to a modern periodic table. The molar mass of ₁₁Na is 22.990. The mass of one mole of Na atoms is 22.990 gram. The mass of 0.5625 moles of Na atoms will be
.
(2 sig. fig. as in the volume of the H₂ gas.)