Question

when the following equation is balanced with the smallest possible integer coefficients, what is the coefficient of H+ in _Cr+ _H+ to _Cr3+_H2

Answer 1

2Cr + 6H^+ ==> 2Cr^3+ + 3H2

Since this is a numbers game I suppose you could call it math but really it isn't. This is a chemistry redox equation. Not only must the coefficients balance but the loss and gain of electrons must balance too.
While I'm answering let me point out that Cr metal (as in this post) reacts with acids, such as HCl, to form Cr^2+ and not Cr^3+ so the equation would read
Cr + 2H^+ ==> Cr^2+ + H2
Happy mathing.