Question

how many molecules are present in 34g of ammonia

Answer 1

no of molecules = $\frac{given  mass }{molar  mass }$×avagadro number 
molar mass of ammonia = atomic mass of nitrogen * 1+ atomic mass of hydrogen*3

14*1+1*3
14+3=17 g

34/17*6.022*$10 ^{23}$=12.044*$10 ^{23}$

Answer 2

molar mass of ammonia = NH₃ = 14 + 1*3 = 14 + 3 = 17 u
1 mole = 17 g
therefore no. of moles in 34 g ,
= given mass / molar mass
= 34/17
= 2 moles

therefore ,

1 mole = 6.022*10²³
2 moles = 6.022*10²³ * 2 = 12.044 * 10²³ 
therefore 34 g of NH₃ contains 12.044*10²³ molecules .

i hope it helps.....