How many grams of water will be produced by complete combustion of $12 \mathrm{g}$ of methane gas

Two elements $\mathrm{A}$ (Atomic mass $75$) and $\mathrm{B}$ (Atomic mass $16$) combine to give a compound having $75.8 \%$ of $\mathrm{A}$. The formula of the compound is

In${\mathrm{CuSO}}_4.5{\mathrm{H}}_2\mathrm{O}$ the percentage of water is _____ $(\mathrm{Cu} = 63.5, \mathrm{S} = 32, \mathrm{O} = 16, \mathrm{H} = 1)$.

When two properties of a system are mathematically related to each other, the relation can be deduced by

Define least count.

What do you mean by significant figures? State the rules for deciding significant figures.

Distinguish between accuracy and precision.