Which alloy is used to prepare scientific balance?

Which of the following fuels has the highest calorific value?

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

State three reasons for the following fact: $(a)$ Magnesium is a metal. One of the reasons must be supported with a chemical equation.

Of the three metals $X, Y$ and $Z$,$X$ reacts with cold water,$Y$ with hot water,and $Z$ with steam only. Identify $X, Y$ and $Z$ and also arrange them in the order of increasing reactivity.

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?