What is the number of electrons lost by a metal atom to form a positive ion called?

Out of the two metals $P$ and $Q$, $P$ is less reactive than $Q$. Suggest an activity to arrange these metals in the order of their decreasing reactivity. Support your answer with a suitable chemical equation.

Make the correct pairs from below mentioned $X$ and $Y$:

$X$	$Y$
$1$. Extraction of sulphur	$p$. Contact process
$2$. Production of nitric acid	$q$. Frasch method
$3$. Production of sulphuric acid	$r$. Haber's process
$4$. Production of ammonia gas	$s$. Ostwald's method

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

Which of the following gases is combustible?

Give reasons for the following:
$(i)$ Carbon can reduce zinc oxide to zinc but not calcium oxide to calcium.
$(ii)$ Copper and aluminium wires are usually used for electricity transmission.