Select the correct passive form of the given sentence.

Buy some apples and grapes for the family.

Let some apples and grapes be bought for the family.

The correct passive form of the given sentence is Let some apples and grapes be bought for the family.

The active voice of the sentence is Buy some apples and grapes for the family. This sentence is in the imperative mood, which is used to give commands or make requests. The passive voice of the sentence is formed by putting the subject of the active sentence after the verb "to be" and the past participle of the main verb. In this case, the subject of the active sentence is "some apples and grapes" and the main verb is "buy." The past participle of "buy" is "bought." So, the passive form of the sentence is Let some apples and grapes be bought for the family.

The other options are incorrect because:

• We should buy some apples and grapes for the family. is in the modal mood, which is used to express necessity or obligation.
• Let us buy some apples and grapes for the family. is in the imperative mood, but it is more informal than the original sentence.
• Some apples and grapes need to be bought for the family. is in the indicative mood, which is used to make statements or ask questions.