Question

The atomic weights of two elements $A$ and $B$ are $40 \,u$ and $80\, u$ respectively. If $x$ g of A contains y atoms, how many atoms are present in $2 x g$ of $B$ :

• A. $\frac{y}{2}$
• B. $\frac{y}{4}$
• C. $y$
• D. $2 y$

Answer 1

Answer: (C)

Number of moles of $A =\frac{ x }{40}$

Number of atoms of $A =\frac{ x }{40} \times$ Avogadro no. $= y$ (say)

Or $x=\frac{40 y}{\text { Avogadro no. }}$

Number of moles of $B =\frac{2 x }{80}$

Number of atoms of B

$=\frac{2 x}{80} \times Av . no =\frac{2}{80} \times \frac{40 y }{ Av . no .} \times Av . no .= y$