Question

Calculate the number of atoms in 3mol helium

Answer 1

 The chemical formula of Helium is He. 

Question 1 : 

Given n = 1.11 x 10^-6 

To get no. of the particle, 
No of particle = no. of mole x Avogadro Constant 
p = n x NA 

1 mol of Helium = 6.02 x 10^23 

No of atoms = (6.02 x 10^23) x (1.11 x 10^-6) 
= 6.66 x 10^17 

................................ 

Question 2 : 

Given p = 4.29x10^21 

p = n x NA 
4.29 x 10^21 = n x (6.02 x 10^23) 
(4.29 x 10^21) / (6.02 x 10^23) = n 
n = Approximately 7.126 x 10^-3 

Hope the answer is right :)