Question

The molar mass of $Ne$ atoms is 20g/mol. How many moles are there in 100g of neon?
A. 5
B. 0.2
C. 2000
D. 10

Answer 1

The molar mass of a substance is the mass (in grams) of a substance in mole of substance. So molar mass is the ratio of given mass of substance and number of moles in that substance.

Complete Step by step answer: In the given question we are given that,
Molar mass of Neon ($Ne$) = 20g/mol
And given mass of Neon ($Ne$) = 100g
We can solve this question by finding out the number of moles of Neon by using the very basic formula of number of moles.
And we know that, molar mass is the ratio of given mass and no. of moles,
That is Molar Mass= given mass/no. of moles
So, No. of moles of neon ($Ne$) = given mass of $Ne$/ Molar Mass of $Ne$
Therefore by putting given values we get,
No. of moles of Neon ($Ne$) = 100g/ (20 g/mol)
Therefore we get, = 5 moles of neon ($Ne$)
So the answer to this question is 5 moles.

So the correct option is A.

Note: Molar mass is the mass of a substance that has 6.022 × ${10^{23}}$ atoms that is one mole. So in the above case no. of atoms of $Ne$is 5$\times$ 6.022$\times$ ${10^{23}}$, that is 30.11 × ${10^{23}}$ atoms. People often get confused about how to find the number of atoms and how they are different from the number of moles.