The picnic for boys are situated by the hill some two hours away from the city.

Correct sentence - The picnic for boys is situated by the hill some two hours away from the city.

The matching of singular verbs with singular subjects and plural verbs with plural subjects is the act of ensuring subject-verb agreement. The verb "are" is plural, and the subject "picnic" is singular. Therefore, the verb "is" agrees with the subject "picnic".

The flowers were put in the holder and situated throughout the office.

Correct sentence - The flowers were put in the holders and situated throughout the office.

We know from the sentence that the apartment has more than one flower. The word "holder" is related to "flowers" and should also be plural; otherwise, it would be illogical that one flower holder could spread throughout an office.

After working for so many years, the chef declared that Jenny’s ability to make delicious soups was better than anyone else.

Correct answer: After working for so many years, the chef declared that Jenny’s ability to make delicious soups was better than anyone else’s skill.

As written, the sentence actually compares this ability with other people (as opposed to those other people’s abilities to make delicious soups). Only by comparing "ability" with "skill" does the sentence make logical sense.

By signing a deal, the parties to the deal each except the terms and conditions.

Correct sentence - By signing a deal, the parties to the deal each accept the terms and conditions.

"Except" and "accept" are examples of homophones. To "accept" something means to consent or receive it, where "except" specifies that something should not be included.