Question

$$\begin{gathered} \mathit{Q}\mathbf{}\mathbf{7}\mathbf{.}TheatomicweightsoftwoelementsAandBare40uand80urespectively.IfxgofAcontainsyatoms,howmanyatoms.Howmanyatomsarepresentin2xgofB? \\ \left(A\right)\frac{y}{2}\left(B\right)\frac{y}{4} \\ \left(C\right)y\left(D\right)2y \end{gathered}$$

Answer 1

Dear Student,

We are given that the atomic masses of the two elements A and B are 40 and 80 respectively. Also, we are given that the number of atoms in amount x g of element A is y. Therefore

number of moles of A in x g of A = mass / molar mass = (x / 40)

number of atoms in x grams of A = number of moles X Avogadro's number

= (x / 40) X 6.023 X 10²³ = y (1)

mass of element B = 2x

number of moles of B in 2x g of B = mass / molar mass = (2x / 80)

number of atoms in 2x grams of B = number of moles X Avogadro's number

= (2x / 80) X 6.023 X 10²³

= (x / 40) X 6.023 X 10²³

But this is equal to y [from (1)]

Therefore the number of atoms in 2x grams of B is the same as x grams of A that is y (Ans:C)

Regards,