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

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

Which of the following weighs the least?

(a) 2 g atom of N

(b) 3 x 10²⁵ atoms of carbon

(c) 1 mole of sulphur

(d) 7 g of silver

Four grams of caustic soda contains:

(a) 6.02 x 10²³ atoms of it

(b) 4 g atom of sodium

(c) 6.02 x 10²² molecules

(d) 4 moles of NaOH