Question

Number of atoms present in 15 g of urea
is
11
H.N-C-NH2
4 NA
3 NA
5 NA
2 NA​

Answer 1

Given mass of urea = 15 grams and Molar Mass of urea = 60 grams.

So, number of moles is:

$moles = \dfrac{given \: mass}{molar \: mass}$

$\implies moles = \dfrac{15}{60}$

$\implies moles = \dfrac{1}{4}$

Now, number of molecules of urea:

$\implies \: molecules = \dfrac{1}{4} \times N_{A}$

Now, each molecule has 8 atoms, hence total atoms in given sample :

$\implies \: atoms = \bigg( \dfrac{1}{4} \times N_{A} \bigg) \times 8$

$\implies \: atoms = 2N_{A}$

Hope It Helps.

Answer 2

Explanation:

Given mass of urea = 15 grams and Molar Mass of urea = 60 grams.

So, number of moles is:

moles = \dfrac{given \: mass}{molar \: mass} moles=

molarmass

givenmass

\implies moles = \dfrac{15}{60} ⟹moles=

60

15

\implies moles = \dfrac{1}{4} ⟹moles=

4

1

Now, number of molecules of urea:

\implies \: molecules = \dfrac{1}{4} \times N_{A}⟹molecules=

4

1

×N

A

Now, each molecule has 8 atoms, hence total atoms in given sample :

\implies \: atoms = \bigg( \dfrac{1}{4} \times N_{A} \bigg) \times 8⟹atoms=(

4

1

×N

A

)×8

\implies \: atoms = 2N_{A}⟹atoms=2N

A

Hope It Helps.