The concentration of H+ ions can be calculated by adding the number of H+ ions from each substance given above. We calculate as follows:
2.5 M HCl ( .01 L ) = 0.25 mol HCl = 0.25 mol H+
0.20 M HNO3 (.50 L ) = 0.1 mol HNO3 = 0.1 mol H+
Therefore,
Concentration of H+ = (0.25 + 0.1) / (.01 +.5) = 0.7 M
Hope this answers the question. Have a nice day.