When he reached home his mother was...(cook)

When he reached home his mother was cooking.

Explanation:

I guess you wanted a correction. :) Have a better day than me.

the central idea of the above passage is following;

central idea: cultural study is very important specially archaeology. grimm's stories very well cater to the importance of cultural relevance.

explanation:

type of error:

the error in the sentence is a "dangling modifier". a dangling modifier is a phrase, word or clause that "dangles" because there is not target to modify. in this case, "after mopping the floor" is the dangling modifier since it has no word to modify. the noun "house" cannot mop the floor; therefore there is a mistake in the writing of the sentence.