Zn(s)+2hcl(aq)-> zncl2(aq)+h2(g)
which statement is true at stp? (the atomic mass of zn is 65.39 u.)
2 mol of hcl produce 1 l of h2 gas.
1 l of zn produces 1l of h2 gas.
65.39 g of zn produce 22.4 l of h2 gas.
1 l of hcl produces 1 mol of h2 gas.

To answer this we need to assume that at STP 1 mol of a substance is equal to 22.4 L. We use this data for the calculations. 
Statement 1
2 mol HCl (1 mol H2 / 2 mol HCl) = 1 mol H2 thus at STP 22.4 L H2
This statement is false.
Statement 2
1 L Zn (1 mol Zn / 22.4 L Zn) (1 mol H2 / 1 mol Zn) (22.4 L H2 / 1 mol H2) = 1L H2
This statement is true.
Statement 3
65.39 g Zn (1 mol Zn / 65.39 g Zn) (1 mol H2 / 1 mol Zn) = 1 mol H2
This statement is true.
Statement 4
1L HCl (1 mol HCl / 22.4 L HCl)(1 mol H2 / 2 mol HCl) = 0.022 mol H2
This statement is false.