What are the substances added to a catalyst to increase its efficiency called?

Give one most suitable word for the following statements.
$(a)$ Metal oxides which show basic as well as acidic behaviour.
$(b)$ Iodine,a non-metal is shining.

When a metal $X$ is treated with cold water, it gives a basic salt $Y$ with molecular formula $XOH$ (molecular mass $= 40$) and liberates a gas $Z$ which easily catches fire. Identify $X$, $Y$, and $Z$, and write the chemical reaction involved.

An element $A$ forms two oxides $AO$ and $AO_2$. The oxide $AO$ is neutral,whereas the oxide $AO_2$ is acidic in nature. Would you call element $A$ a metal or a non-metal?

Generally, metals react with acids to produce salt and hydrogen gas. Which of the following acids does not produce hydrogen gas when reacting with most metals (except $Mn$ and $Mg$)?

In the electrolytic refining of metals, the insoluble impurities present in the impure metal settle down at the bottom of the container below the anode. What is this called?