Two-fifth of a container is filled with blue liquid, one-third of the remaining container is filled with black liquid, five-sixth of the still remaining container is filled with yellow liquid and the remaining 4.2 litres is of white colour. Find the total capacity of the container.

The correct option is 63 litres.

Let the total capacity of the container be $V$ litres.

We will determine the remaining capacity step-by-step as each liquid is filled into the container.

Step 1: Blue Liquid
Two-fifth of the container is filled with blue liquid.
Volume of blue liquid = $\frac{2}{5}V$
Remaining volume after filling blue liquid = $V-\frac{2}{5}V=\frac{3}{5}V$

Step 2: Black Liquid
One-third of the remaining container is filled with black liquid.
Volume of black liquid = $\frac{1}{3}\×\frac{3}{5}V=\frac{1}{5}V$
Remaining volume after filling black liquid = $\frac{3}{5}V-\frac{1}{5}V=\frac{2}{5}V$

Step 3: Yellow Liquid
Five-sixth of the still remaining container is filled with yellow liquid.
Volume of yellow liquid = $\frac{5}{6}\×\frac{2}{5}V=\frac{1}{3}V$
Remaining volume after filling yellow liquid = $\frac{2}{5}V-\frac{1}{3}V=\frac{6-5}{15}V=\frac{1}{15}V$

Step 4: White Liquid and Total Capacity
The remaining volume is filled with white liquid, which is given as 4.2 litres.
Therefore,
$\frac{1}{15}V=4.2$

Multiplying both sides by 15 gives:
$V=4.2\×15$
$V=63\text{litres}$

Thus, the total capacity of the container is 63 litres.