Barrons SAT Subject Test Chemistry, 13th Edition

60. (E) H 2 to O 2 ratio by volume is 2 : 1 in the formation of water. Therefore,

4.0 mL H 2 will react with 2.0 mL of O 2 to make 4.0 mL of steam.

2H 2 (g) + O 2 (g) → 2H 2 O(g)

This leaves 30. mL of O 2 uncombined.