Question

The number of gram molecules of oxygen in $6.02 \times {10^{24}}$ $CO$ molecules is:
(A) $10$ gram molecules
(B) $5$ gram molecules
(C) $1$ gram molecules
(D) $0.5$ gram molecules

Answer 1

Number of moles: It is defined as the ratio of mass of the substance to the molecular mass of the substance. One mole of substance contains $6.022 \times {10^{23}}$ which is equal to ${N_A}$ .

Complete step by step solution:
Gram molecule: It is defined as the number of grams of the substance i.e. the molecular mass of the substance.
Atomic mass: It is defined as the total number of protons and neutrons present in the nucleus of an atom. It is represented by symbol A.
Atomic number: It is defined as the number of protons in the nucleus of an atom. It is represented by symbol Z.
Molecular weight of the substance: It is defined as the sum of the molecular masses of all elements present in the substance.
Now the number of gram atoms in $6.02 \times {10^{24}}$ $CO$ molecules will be $\dfrac{{6.02 \times {{10}^{24}}}}{{6.02 \times {{10}^{23}}}} = 10$
The number of gram molecules of oxygen in $6.02 \times {10^{24}}$ carbon monoxide molecule is $\dfrac{{10}}{2} = 5$ because one oxygen molecule is made of two atoms of oxygen. Hence the number of gram atoms is divided by two.
So, the number of gram molecules of oxygen in $6.02 \times {10^{24}}$ $CO$ molecules is $5$ gram molecules.
Hence option B is correct.

Note:
Formula mass: It is defined as the sum of the atomic weights of all the atoms present in the compound. And if the compound is covalent in nature then the formula mass is known as molecular mass and if we are calculating mass of one mole of substance then it is known as molar mass.