$H_2S$ reacts with $O_2$ to form:

Identify the catalyst $(A)$ used in the following reaction:
$CO + H_2O \rightleftharpoons CO_2 + H_2$

What do you understand by the term "non-stoichiometric hydrides"? Do you expect this type of the hydrides to be formed by alkali metals? Justify your answer.

Which chemical is used as a refrigerant in refrigerators?

Given below are two statements:
Statement $I$ : Nickel is being used as the catalyst for producing syn gas and edible fats.
Statement $II$ : Silicon forms both electron rich and electron deficient hydrides.
In the light of the above statements,choose the most appropriate answer from the options given below:

$TiH_{1.73}$ is an example of