In a closed vessel at $STP$,$50 \, L$ of $CH_4$ is ignited with $750 \, L$ of air (containing $20 \% \ O_2$). The number of moles of $O_2$ remaining in the vessel on cooling to room temperature is closest to

$108 \ g \ Al$ and $213 \ g \ MnO$ were heated to initiate the reaction:
$2 Al + 3 MnO \to Al_2O_3 + 3 Mn$
Which of the following is correct? (Atomic weights: $Mn = 55$,$Al = 27$)

At $NTP$,if $100 \ mL$ of $N_2$ and $100 \ mL$ of $H_2$ are mixed together in a container,what will be the volume of $NH_3$ formed in $mL$?

What will be the volume of the mixture after the reaction? $litre$
$NH_3(4 \ litre) + HCl(1.5 \ litre) \to NH_4Cl(s)$

$CaCO_3 + 2HCl \to CaCl_2 + CO_2 + H_2O$ ; In this chemical reaction,what will be the amount of calcium chloride formed when $10 \ g$ of calcium carbonate and $400 \ mL$ of $0.25 \ M$ $HCl$ are used? (Atomic masses: $Ca=40, C=12, O=16, H=1, Cl=35.5$)

In Ostwald's process for the manufacture of nitric acid,the first step involves the oxidation of ammonia gas by oxygen gas to give nitric oxide gas and steam. What is the maximum weight of nitric oxide that can be obtained starting only with $10.00 \, g$ of ammonia and $20.00 \, g$ of oxygen?