Which of the following elements is less reactive than hydrogen?

• A. Calcium
• B. Lead
• C. Magnesium
• D. Sodium

Answer: (B)

You're being tested on the reactivity series and how hydrogen is used as a reference point. In this series, metals are ordered by how readily they lose electrons. Metals higher up react more readily and can displace hydrogen from acids or react with water, while metals lower down are less reactive and do not displace hydrogen under normal conditions.

Calcium, magnesium, and sodium sit above hydrogen, so they are more reactive and will readily release hydrogen gas when they react with acids (and, in some cases, with water). Lead lies below hydrogen, so it is less reactive than hydrogen and does not displace hydrogen from acids in typical reactions. This is why lead is the one less reactive than hydrogen.