# A student wants to have 3.011 × 1023 atoms each of magnesium and carbon elements. For this purpose, he will have to weigh :(a) 24 g of magnesium and 6 g of carbon(b) 12 g of carbon and 24 g of magnesium(c) 20 g of magnesium and 10 g of carbon(d) 12 g of magnesium and 6 g of carbon

Correct Answer: (d) 12 g of magnesium and 6 g of carbon

Explanation: 12 g of carbon and 24.3 g of magnesium, each contains 6.022×1023 number of atoms.

Let X g of carbon have 3.011×1023 number of atoms.
Therefore,
X= $\frac {molar \ mass \ of \ carbon × number \ of \ atoms \ of\ carbon} {Avogadro \ number}$
X =12×3.011×1023 / 6.022×1023
X=6 g of carbon
So, 6 g of carbon contains 3.011×1023 number of atoms.
Now,
Let X g of magnesium have 3.011×1023 number of atoms.
Therefore,
X= $\frac {molar \ mass \ of \ magnesium × number \ of \ atoms \ of\ magnesium} {Avogadro \ number}$
X=24 × 3.011×1023/ 6.022×1023
X=12 g of magnesium
So, 12 g of magnesium contains ​3.011×1023 number of atoms.

Therefore, the student will weigh 12 g of magnesium and 6 g of carbon.

Updated on: 10-Oct-2022

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