1 bottle of honey costs Rs 240 but a pack of 4 of the same bottles costs Rs 768. What is the effective discount (in %) on the pack?

The marked price of one bottle is Rs 240.

If the bottles are bought individually, the cost of 4 bottles would be $$4 \times 240 = 960$$ rupees.

The pack of 4 bottles is offered for Rs 768.

Hence, the amount of discount on the pack is $$960 - 768 = 192$$ rupees.

Discount percent is computed by the formula
$$\text{Discount \%} = \frac{\text{Discount}}{\text{Marked Price}} \times 100$$

Substituting the values:
$$\text{Discount \%} = \frac{192}{960} \times 100 = 20\%$$

Therefore, the effective discount on the pack is 20 percent.

Option D which is: 20