Question

If the mass of 0.25 moles of an element X is 2.25 g the mass of one atom of X is about???

Answer 1

Answer:  $1.66\times 10^{-23}g$

Explanation: According to avogadro's law, 1 mole of every substance occupies 22.4 Liters at STP and contains avogadro's number $6.023\times 10^{23}$ of particles.

Given moles = 0.25

1 mole = $6.023\times 10^{23}$ atoms of an element X

0.25 moles= $\frac{6.023\times 10^{23}}{1}\times 0.25=1.50\times 10^{23}$ atoms of element X= 2.5 g

Thus $1.50\times 10^{23}$ atoms of element X weigh 2.5 g

So 1 atom of element X will weigh = $\frac{2.5}{1.50\times 10^{23}}\times 1=1.66\times 10^{-23}g$

Answer 2

Option A is the right answer

Mass of 0.25NA atoms of X is 2.25gram

so,mass of 1 atom is=

2.25/0.25NA gram

= 1.5×10*-23 gram

* I hope it will help you*