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

Who discovered hydrogen gas?

Balance the following chemical equations and identify the type of chemical reaction.
$(a)$ $TiCl_4(l) + Mg(s) \to Ti(s) + MgCl_2(s)$
$(b)$ $CaO(s) + SiO_2(s) \to CaSiO_3(s)$
$(c)$ $H_2O_2(l) \xrightarrow{UV} H_2O(l) + O_2(g)$

Why is respiration considered an exothermic reaction? Explain.

What is the basic raw material used in the Contact Process for the production of sulfuric acid?

Name the type of reaction for the following:
$(i)$ Silver items turning black when left exposed to air.
$(ii)$ Change in colour of copper sulphate from blue to green on dipping an iron nail in it.