Chains, Ropes, and Slings Test I Source: Questions and answers from the National Safety Council Progress Indicator: Question 6 of 20 6.  The explosive range of hydrogen, for example, is __________ percent in the presence of normal air. Choices: 3.0 to 75.2 5.0 to 76.3 4.0 to 72.2 4.0 to 74.2