Question

the atomic mass of two elements A and B are 20 and 40 respectively if Xg of A contains Y atoms how many atoms are present in 2Xg of B

Answer 1

In case of same number of atoms,
(Mass of A) : (Mass of B) = 20 : 40 = 1 : 2

Now, (Mass of A) : (Mass of B) = x : 2x = 1 : 2
Then, they have the same number of atoms, i.e.
There are Y atoms of B.

Answer 2

Answer: Y atoms

Explanation:

According to avogadro's law, 1 mole of every substance weighs equal to the molecular mass and contains avogadro's number $6.023\times 10^{23}$ of particles.

$Moles=\frac{\text{Given mass}}{\text{Molar mass}}$

Moles of A=$\frac{X}{20}=0.05\times Xmoles$  

Thus $0.05\times X$ moles of A contain = Y atoms

Moles of B=$\frac{2X}{40}=0.05Xmoles$  

Thus $0.05\times X$ moles of B contains = Y atoms

As equal moles contain equal atoms.