If the reduction of a sample of $Cu_2O$ yields $1.27 \, g$ of $Cu$,then how many grams of oxygen must be present in it?

At $400 \ K$,$1 \ mol$ of a hydrocarbon is completely burned. It produces $132 \ g$ of a gas along with $72 \ g$ of water vapour. The hydrocarbon is:

How many grams of $NaOH$ are required to neutralize $12.2 \ g$ of benzoic acid (in $g$)?

How many grams of $BaCO_3$ are produced when excess $CO_2$ is passed through $0.205 \ mol$ of $Ba(OH)_2$?

An iron alloy contains $54.7\%$ iron and has a density of $8.17 \, g \, cm^{-3}$. What is the number of iron atoms in an alloy block of dimensions $10 \, cm \times 15 \, cm \times 20 \, cm$?

In $Fe_{0.96}O$,$Fe$ is present in $+2$ and $+3$ oxidation states. What is the mole fraction of $Fe^{2+}$ ions in the compound?