A student puts his signature with a graphite pencil. If the mass of carbon in the signature is 10^-12g, calculate the number of carbon atoms in the signature. 

An unknown gas shows a density of $3$ gram per litre at $273°\mathrm{C}$ and $1140 \mathrm{mm}$ $\mathrm{Hg}$ pressure. What is the gram molecular mass of this gas? 

Cost of Sugar (${\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}$) is ₹$40$ per $\mathrm{kg}$. Calculate its cost per mole. 

Which of the following weighs the least? 

Correct the statement, if required:

One mole of chlorine contains $6.023\times {10}^{23}$ atoms of chlorine.

Correct the statement, if required:

Under similar conditions of temperature and pressure, two volumes of hydrogen combined with two volumes of oxygen will give two volumes of water vapour.

Correct the statement, if required :

The relative atomic mass of an element is the number of times one molecule of an element is heavier than $\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$12$}\right.$ th the mass of an atom of carbon $\left[{\mathrm{C}}^{12}\right]$.