Q178
General ScienceChemistry
If number of molecules present in 9g of water is $n$, then number of molecules present in 44g of carbon-di-oxide is
- a.$n$
- b.$2n$
- c.$\dfrac{n}{2}$
- d.$3n$
Answer: (B) $2n$
The molar mass of water is 18 g, so 9 g of water is 0.5 mole and contains $n$ molecules. The molar mass of carbon dioxide is $12+2\times16=44$ g, so 44 g is 1 mole, which contains twice as many molecules as half a mole, i.e. $2n$. Equal numbers of moles, not equal masses, contain equal numbers of molecules. One mole of any substance has $6.022\times10^{23}$ particles (Avogadro's number), and one mole of any gas occupies 22.4 litres at STP.