How many grams of bromine are required to react with $21 \ g$ of $C_3H_6$? (Atomic mass of $Br = 80$)

How many grams of $Cu(NO_3)_2$ are needed to obtain $1 \ g$ of copper? $($ Atomic mass: $Cu = 63.5, N = 14, O = 16$ $)$

At $S.T.P.$, the volume of $7.5 \ g$ of a gas is $5.6 \ L$. The gas is

$40\%$ of a mixture of $0.2 \ mol$ of $N_2$ and $0.6 \ mol$ of $H_2$ reacts to give $NH_3$ according to the equation:
$N_{2(g)} + 3H_{2(g)} \rightleftharpoons 2NH_{3(g)}$
at constant temperature and pressure. What is the ratio of the final volume to the initial volume of gases?

How much lime $(CaO)$ can be obtained by heating $200 \ kg$ of limestone which is $95 \%$ pure? ............... $kg$

$4.0 \,g$ of $NaOH$ are contained in one decilitre of solution. Its molarity would be ......... $M$.