What is the mass (in grams) of a CO_2 gas sample that occupies 5.46 L at STP?

10.7g of

Explanation:

Any gas at STP occupies 22.4 L/mol.

As such:

5.46/22.4 = 0.244 mol of

mass = mol * molecular weight = 0.244 * 44 = 10.7g of

First step is always balance the equation:
n2h4 + 7 h2o2 --> 2hno3 + 8h2o 

so assuming that n2h4 is in excess and only moles of h2o2 are determining the product content then 7 moles of h2o2 give 2 moles of hno3
so:
7: 2
x: 0.08
x=0.28 moles of h2o2