Question

Largest number of molecules are present in:
A. $44gm$ of carbon dioxide
B. $28gm$ of carbon monoxide
C. $36gm$ of water
D. $64gm$ of sulphur dioxide

Answer 1

Hint : To find out which molecule will have the largest number of molecules, first try to calculate the number of moles of each compound given. The compound having the largest number of mole values will have the largest number of molecules.

Complete step by step solution:
As per the given question, we have to find out the compound having the largest number of molecules.
We should know that the compound which will have the highest value for the number of moles will have the largest number of molecules.
And, we know that the number of moles of a substance equals the ratio of the mass given for the substance to that of its molecular weight. So, let's calculate the number of moles of each compound given in the options.
(i) Mass of carbon dioxide ($C{{O}_{2}}$) is given as $44gm$.
The molecular weight of carbon dioxide is $12\times 1+16\times 2=44gm$.
So, the number of moles will be $=\dfrac{\text{mass given}}{\text{molecular weight}}=\dfrac{44}{44}=1\text{ mole}$.
(ii) Mass of carbon monoxide ($CO$) is given as $28gm$.
And, the molecular weight of carbon monoxide is $12\times 1+16\times 1=28gm$.
So, the number of moles will be $=\dfrac{28}{28}=1\text{ mole}$.
(iii) Mass of water (${{H}_{2}}O$) given is $36gm$.
And, the molecular weight of water is $1\times 2+16\times 1=18gm$.
So, the number of moles of water will be $=\dfrac{36}{18}=2\text{ moles}$.
(iv) Mass of sulphur dioxide ($S{{O}_{2}}$) given is $64gm$.
And, the molecular weight of sulphur dioxide is $32\times 1+16\times 2=64gm$.
So, the number of moles for this compound will be $=\dfrac{64}{64}=1\text{ mole}$.
As we can see that, water has the highest value for the number of moles in respect to other compounds.
So, the largest number of molecules are present in water.

Hence, the correct option is C.

Note: It is important to note that, Avogadro’s number is generally used to calculate the number of molecules present in any given mass of compound, in which one mole of a compound (may be atom, molecule) equals to $6.023\times {{10}^{23}}$ of number of molecules.