Question

The total number of electrons in 2.0g D2o to that of 1.8 gm h20

Answer 1

1 mole of D2O and H2O has 10moles of electrons 
 2g of D2O = 2/20 = 0.1 mole 
 1.8 g of H2O = 1.8 / 18 = 0.1 mole 
hence the no. of electrons in both the molecules are =  0.1 x 10 moles of electrons = 6.023 x 10^23 electrons

Answer 2

The number of electrons of $D_2O$ and $H_2O$ is $6.022 \times 10^{23}$

Given:

Mass of $D_2O$ = 2.0 g

Mass of $H_2O$ = 1.8 g

Solution:

$\text{Number of electrons} = \text{Atomic number} \times \text{Number of atoms}$

For $D_2O$:

$\text{ Atomic number } =(2 \times 1)+(1 \times 8)=2+8=10$

$\text {Number of moles} =\text {Mole} \times \text {Avogadro number}$

$\Rightarrow \text { Number of moles }=\frac{\text { Mass of substance }}{\text {Mass of one mole}} \times \text {Avogadro number}$

$\therefore \text { Number of moles }=\left(\frac{2}{(2 \times 2)+16}\right) \times 6.022 \times 10^{23}$

Thus,

$\text {Number of moles} =(0.1) \times 6.022 \times 10^{23}=6.022 \times 10^{22}$

$\text{Number of electrons} =10 \times 6.022 \times 10^{22}$

$\Rightarrow \text { Number of electrons }=6.022 \times 10^{23}$

For $H_2O$:

$\text{ Atomic number } =(2 \times 1)+(1 \times 8)=10$

$\Rightarrow \text { Number of moles }=\left(\frac{1.8}{(2 \times 1)+16}\right) \times 6.022 \times 10^{23}$

$\therefore \text { Number of moles }=6.022 \times 10^{22}$

Thus, the number of electron is,

$\text { Number of electrons }=10 \times 6.022 \times 10^{22}$

$\Rightarrow \text { Number of electrons }=6.022 \times 10^{23}$