1. I have two dogs.
One is black, and the other is black and white.
2. I have two dogs.
One is black, and the second is black and white.
(Which expression is correct? Can we use 'the second' instead of 'the other' here?)
Yes. Both sentences are correct. But the first sentence is probably the best.
2.I have two dogs.One is black, and the second is black and white.
Both expressions are correct, but they convey slightly different meanings.
1. "I have two dogs. One is black, and the other is black and white."
In this sentence, "the other" refers to the second dog in relation to the first dog mentioned. It implies that there are only two dogs, and the speaker is indicating the difference in color between the two.
2. "I have two dogs. One is black, and the second is black and white."
In this sentence, "the second" is used to specifically identify the second dog without implying a direct comparison to the first dog. It doesn't limit the number of dogs to just two, and it could imply there are more than two dogs in total.
Both expressions are grammatically correct, but the choice between "the other" and "the second" depends on the intended meaning and context of the statement.