Question

Which metal would you expect to generate more gas when exposed to a weakly acidic solution, K or Ca?

I say K because it only needs to lose one electron. Is this true?

Answer 1

That sounds about right. K is more unstable, and reacts more readily.

Answer 2

Wouldn't the amount of gas generated depend upon the AMOUNT of K or Ca used? And when you say more H2 gas, is that more volume or more mass?
On a mol basis, Ca generates 1 mol H2 gas per 1 mol Ca used while K generates 1 mol H2 gas per 2 mols K used.
The equations are (HA is a weak acid).
2K + 2HA ==> 2KA + H2
Ca + 2HA ==> CaA2 + H2.

You need to calculate the amount of H2 gas for the same mass of K vs Ca.