We know that, in a pack of 52 cards 26 are of red colour and 26 are of black colour.
It is given that 2 cards are accidentally dropped
[Here, we take 51 because already one card is dropped. So, we left with 51 cards]
Similarly,
Probability of dropping a black card first = 26/52
Probability of dropping a black card second = 26/51
∴ P(both cards of different colour)
Hence, the correct option is (C).