Select the option that expresses the given sentence in passive voice.

Siddharth is floating a grand plan by next week.

A grand plan is being floated by Siddharth next week.

The correct option that expresses the given sentence in passive voice is A grand plan is being floated by Siddharth next week.

The other options are incorrect because:

• Siddharth is being floated by a grand plan next week is grammatically incorrect. The verb "to float" is intransitive, which means that it does not take a direct object. Therefore, it cannot be used in the passive voice.
• Next week is keeping afloat by Siddharth’s grand plan is grammatically incorrect. The verb "to keep afloat" is transitive, which means that it takes a direct object. However, the subject of the sentence is "next week," which is not a thing that can be kept afloat.
• A grand plan is being floating by Siddharth next week is grammatically incorrect. The verb "to float" is intransitive, which means that it does not take a direct object. Therefore, the preposition "by" is not necessary in the passive voice.