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# The atomic masses of two elements P and Q are 20 and 40 respectively . If $'a'g$ of P contains $'b'$ atoms , how many atoms are present in $'2a'g$ of Q .A.aB.bC.2aD.2b

Last updated date: 14th Sep 2024
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Hint:According to Avogadro's hypothesis equal volumes of all gases under similar conditions of temperature and pressure contain equal numbers of atoms or molecules.

The given masses of P and Q are 20 and 40 respectively.
Let us first take out the number of moles in $'a'g$ of P
Number of moles = $\dfrac{w}{M}$ where w = given mass and M = molecular mass
Number of atoms = ${N_ \circ } \times moles$ where ${N_ \circ } =$ Avogadro's number

In case of P number of atoms = $\dfrac{a}{{20}} \times {N_ \circ } = b$ (equation 1)
Now , number of atoms in Q = $\dfrac{{2a}}{{40}} \times {N_ \circ } = \dfrac{a}{{20}} \times {N_ \circ }$ (equation 2)

On substituting the value of $\dfrac{a}{{20}} \times {N_ \circ }$ from equation 1, we get
therefore , Number of atoms in $'2a'g$ of Q = b

Therefore option B is correct.