The problem does not state the quantity of sulfuric acid. If none is present, then the reaction will not be able to produce any hydrogen. But let's solve it for the maximum amount of hydrogen gas. You have the chemical equation, Ca + H2SO4 -> CaSO4 + H2, which is balanced already. This equation tells you that for every atom of Ca, you get one molecule of H2 gas. The number of atoms of Ca is not given, but we are given the mass of the Ca metal, which is 102 g. This can be converted to "moles." A mole is a number of molecules or atoms of something. Using moles makes problems like this much more convenient, because atoms are very tiny, so there are a lot of them in 102 g. So, anyway, to convert grams to moles of an atom, you need the atomic mass (in the case of a molecular substance, you would likewise use molar mass). One atom of Ca metal weighs 40.078 u, or, in other words, one mole of Ca metal weighs 40.078 grams. 102 grams divided by 40.078 grams per mole gives 2.54504 moles of Ca. Since the ratio of Ca:H2 in the equation is 1:1, or, in other words, one mole of Ca yields up to one mole of H2, 2.54504 moles of Ca yields anything up to 2.54504 moles of H2. But the question asks for volume at STP, not moles, so we also have to convert from moles to liters. If you look in a table (probably in your textbook, if not, they are available online), one mole of H2 gas at STP takes up 22.4 L of space at STP. Multiply the 22.4 L/mol times the 2.545037 moles and you get 57.0 L of H2 gas at STP. So, if there is an excess of H2SO4, and you are able to recover 100% yield, you should get 57.0 L of hydrogen gas. If the amount of sulfuric acid is something less than 2.545037 moles, or greater than zero, then you'll have to either work it out yourself or let me know so I can help.