Which of the following metal does not produce H2 gas after reaction with dil. acid ?A Mg B Na C K D Cu

The metal that does not produce H2 gas after reaction with dilute acid is Copper (Cu). Here's why:

When a metal reacts with a dilute acid, the metal displaces hydrogen from the acid to produce a salt and hydrogen gas. This is a typical example of a displacement reaction. However, not all metals can displace hydrogen from acids.

The reactivity of metals decreases down the metal reactivity series, which is an empirical series ranking of metals according to their reactivity from most reactive to least reactive.

Copper (Cu) is a low reactivity metal and is located towards the bottom of the reactivity series. Therefore, it does not have enough reactivity to displace hydrogen from the acid. As a result, no hydrogen gas is produced when copper reacts with a dilute acid.

So, the correct answer is D. Copper (Cu).