Question

Number of molecules in 7.4 gram of ninhydrin

Answer 1

Molecular weight or mass of  NinHydrin =  9 * 12 + 6 * 1 + 16 * 4 
  = 178

As per Avogadro's law we have that one mole ( 178 gms) of NonHydrin contains N = avogadro number ie., 6.023 * 10²³ molecules.

so number of molecules in 7.4 gms are:  6.023 * 10²³ * 7.4 / 178
       = 2.502 * 10²² 

Answer 2

Chemical formula of Ninhydrin is C₉H₆O₄ 
Molar mass = 9×12 + 6×1 + 4×16 = 108+6+64 = 178g

178 gram of Ninhydrin contains = 1 mole = 6.022×10²³ molecules
1 gram of Ninhydrin contains = 6.022×10²³/178 molecules
7.4 gram of Ninhydrin contains = 7.4×6.022×10²³/178 = 2.561×10²² molecules

So number of molecules in 7.4 gram Ninhydrin is 2.561×10²² molecules.