Explanation:

Hydrogen is a highly reactive gas and it easily reacts with many elements. However, it does not react directly with certain elements like Na, Zn, K, and Ca. This is due to the following reasons:

Electronic configuration:

The outermost electronic configuration of hydrogen is 1s¹ and it requires one more electron to complete its duplet. On the other hand, the outermost electronic configuration of Na, Zn, K, and Ca are 3s¹, 3d¹⁰4s², 4s¹, and 4s², respectively. These elements have a completely filled valence shell and do not need to gain or lose electrons to attain stability. Thus, there is no driving force for hydrogen to react with these elements.

High ionization energy:

Na, Zn, K, and Ca have high ionization energies, which means that it requires a lot of energy to remove an electron from these elements. Hydrogen does not have the energy to overcome this barrier and react with these elements.

Formation of stable compounds:

Na, Zn, K, and Ca form stable compounds with other elements such as oxygen, chlorine, and sulfur. These compounds are more stable than any compound that can be formed with hydrogen. Thus, there is no need for these elements to react with hydrogen.

In conclusion, hydrogen does not react directly with Na, Zn, K, and Ca due to their electronic configuration, high ionization energy, and the formation of stable compounds.