There are D) 9.51E23 
Further explanation
Given
1.58 moles of LiOH
Required
The number of formula units
Solution
The mole is the number of particles(molecules, atoms, ions, formula units) contained in a substance 
1 mol = 6.02.10²³ particles 
Can be formulated 
N=n x No 
N = number of particles 
n = mol 
No = Avogadro's = 6.02.10²³ 
So for 1.58 moles :
= 1.58 x 6.02 x 10²³ 
= 9.5116 x 10²³