Question

The number of water molecules present in a drop of water (volume 0.0018 ml) at room temperature is
(a) 1.084 × 10¹⁸
(b) 6.023 × 10¹⁹
(c) 4.84 × 10¹⁷
(d) 6.023 × 10²³

Answer 1

6.023^24 are there in 1 mole of water.

Answer 2

Answer :

Option (b) 6.023 × 10¹⁹ is the correct option.

Solution :

Given volume of water = 0.0018 ml

We know, density = 1 g/ml.

So,

$=>Density = \dfrac{mass}{volume} \\ \\ = > 1 = \dfrac{mass}{0.0018} \\ \\ = > 0.0018 \: g = mass$

Hence, mass of a drop of water = 0.0018 g

Now,

$Number \: of \: moles (n) = \frac{given \: mass}{molar \: mass} \\ \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = \frac{0.0018}{18} \\ \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = {10}^{ - 4} \: moles$

Therefore,

Number of molecules = 6.023×10²³×10¯⁴

Number of molecules = 6.023 × 10¹⁹