Question

why hydrogen is neutral to litmus

Answer 1

Hydrogen exists independently as hydrogen molecule (H2). It is a neutral molecule, therefore, it does not have any effect on the litmus paper.
But, whereas, if it is H+ ions (from an acidic solution): it would turn the blue litmus to red.
The hydrogen gas is a neutral gas.

Answer 2

Answer:

Hydrogen exists independently as hydrogen molecule (H2). It is a neutral molecule, therefore, it does not have any effect on the litmus paper. But, whereas, if it is H+ ions (from an acidic solution): it would turn the blue litmus to red. The hydrogen gas is a neutral gas.