1.Br2(g) + ___H2O(l) + ___SO2(g) ---> ___HBr(aq) + ___H2SO4(aq)

Answer 1

This is a redox equation,notice the valences are

left right change
Br 0 -1 gained one electron per
S +4 +6 lost two electrons

so for every S, there has to be two Br on the left. With just Br2, that means that coefficient is the same as SO2.

Br2 + XX H2O + SO2>> YYHBr + H2SO4
the YY becomes 2 to balance the left side,

Br2 + XX H2O + SO2>>2 HBr + H2SO4

which now balancing the H on each side, means XX is 2