The ratio of juice to water in container B is 4 : 3, respectively. 21 liters of the mixture is taken out and poured into an empty container C. If 4 liters of pure juice are added to container C, then find the difference between the quantities of juice and water in container C (in liters).

The correct option is 7 (or Option 7 liters).

Step 1: Understand the initial ratio in container B
The ratio of juice to water in container B is given as $4:3$.

When a mixture is drawn from a container, the ratio of its components (juice and water) in the removed portion remains the same as in the original container.

Step 2: Find the quantities of juice and water taken out
Total volume of mixture taken out = $21\text{ liters}$

Total parts of the ratio = $4+3=7\text{ parts}$

Quantity of juice taken out and poured into container C:
$\text{Juice in C initially}=\frac{4}{7}\times 21=12\text{ liters}$

Quantity of water taken out and poured into container C:
$\text{Water in C}=\frac{3}{7}\times 21=9\text{ liters}$

Step 3: Account for the added pure juice
4 liters of pure juice are added to container C.
$\text{New quantity of juice in C}=12+4=16\text{ liters}$
$\text{Quantity of water in C}=9\text{ liters}$

Step 4: Calculate the difference between juice and water in container C
$\text{Difference}=16-9=7\text{ liters}$

Thus, the difference between the quantities of juice and water in container C is 7 liters.