How many kilograms of $CaCO_3$ must be heated to obtain $56$ kilograms of $CaO$? [Atomic masses: $Ca = 40, C = 12, O = 16$]

$A$ metal chloride contains $55.0 \%$ of chlorine by weight. $100 \ mL$ of vapours of the metal chloride at $STP$ weigh $0.57 \ g$. The molecular formula of the metal chloride is $...$. (Given: Atomic mass of chlorine is $35.5 \ u$)

$100 \ mL$ of $PH_3$ when completely decomposed produces phosphorus and hydrogen. The change in volume of the gas is
$PH_{3(g)} \longrightarrow P_{(s)} + \frac{3}{2} H_{2(g)}$

$23 \ g$ of $Na$ metal reacts with ethanol to produce which of the following?

If a $100 \ mL$ solution contains $X \ g$ of $Na_2CO_3$ and its concentration is $Y \ M$,then $X$ and $Y$ are respectively ..............

The minimum amount of $O_2\,(g)$ consumed per gram of reactant is for the reaction: (Given atomic mass: $Fe = 56, O = 16, Mg = 24, P = 31, C = 12, H = 1$)