Which pair of substances generates hydrogen gas upon reaction?

Copper metal with concentrated nitric acid
Gold metal with sodium cyanide solution in the presence of oxygen
Zinc metal with sodium hydroxide solution
Iron metal with concentrated nitric acid

Correct answer: Zinc metal with sodium hydroxide solution

Solution

The reaction between zinc metal and sodium hydroxide solution generates hydrogen gas, as zinc is more reactive than hydrogen and can displace it from the sodium hydroxide solution, producing zinc oxide and releasing hydrogen gas.

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