Question

How many moles are found in a 3.8g sample of NaBH4

Answer 1

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 The number of mole is defined by the ratio of mass or weight of the substance to the molar mass of substance or compound

As Number of moles = Mass of substance/molar mass of substance

As the mass here is 3.8 grams while the number of moles of NaBH4(sodium borohydride) is 37.83g/mol. we are taking the round about value of molar mass as 38 here.
So putting values in formula :
Number of moles of NaBH4= Mass or weight of NaBH4/molar mass of NaBH4
Number of moles of NaBH4= 3.8/38 = 0.1 moles 
So 0.1 moles will be present in 3.8 grams of NaBH4.

Answer 2

Given compound SODIUM Boron Hydride.
NaBH4.
Molecular mass of NaBH4
= sum of atomic masses of Na + atomic mass of B+ Atomic mass of H
= 23+11+4×1
=23+11+4
=38 unified mass
Therefore molar mass of NaBH4= 38g
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Formula to be used:
Number of moles =Given weight/ molar mass
=3.8/38
=38/38*10
=0.1 moles
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THEREFORE NUMBER OF MOLES IN 3.8g of NaBH4 is 0.1