The given sentence is in active form of present interrogative tense. The structures for active/passive voices are:

Active: Wh-question word + do/does + subject + verb (Ist form) + object…?

Passive: Wh-question word + Is/are/am + object + verb (IIIrd from) + by + subject…?

So, with the help of the above structures, we can convert the given sentence into passive voice: Why is he liked by you so much?

Hence, option C is the correct answer. 

The given sentence is of present perfect tense and it is in active form. The structures for active/passive voices are:
 

Active: Subject + has/have + verb (IIIrd form) + object...
 

Passive: Object + has/have + been + verb (IIIrd form) + by + subject...
 

So, the passive voice of the given sentence would be: A new car has been bought by me.

Hence, option C is the correct answer. 

The given sentence is in active voice. It is of present indefinite interrogative tense. The structures for active/passive voices are:
 

Active: Do/does + Subject + verb (Ist form) + object…
 

Passive: Is/are/am + Object + verb (IIIrd form) + by + subject…
 

So, based on the above structures, we can convert the given sentence into passive voice: Is what I mean understood by you?

Hence, option C is the correct answer. 

There are some verbs which can take two objects, for example-

He gave me some money.

You presented her a ring.

There are two objects in these sentences. See:

Gave             me               some money

Presented     her               a ring

The verbs which takes single object are called mono-transitive verbs. For example-

They betrayed you.

The verbs which takes two objects are called Di-transitive verb. The passive voice of sentences which have Di-transitive verbs can be made using any of the two objects.

“Give” is a di-transitive verb, so the passive voice of the question sentence can be made in two ways:

Active: Mohan gave the beggar an old shirt.

Passive: 1. An old shirt was given to the beggar by Mohan.

             2. The beggar was given an old shirt by Mohan.

Hence, option B is the correct answer.

The given sentence is the passive form of present perfect tense. The structures for passive/active voices are:

Passive: Object + has/have + been + verb (IIIrd form) + by + subject...

Active : Subject + has/have + verb (IIIrd form) + object...

So, the active voice of the given sentence would be:

The chairman has called off the meeting.

Rules for changing the direct speech into indirect speech are given below:-

Says to/said to changes to tells/told in indirect speech.

Inverted commas (" ") are removed.

The words like, this, these, tomorrow, yesterday change to that, those, the next day, the previous day respectively.

Tense will remains the same.

Second-person pronoun changes according to the subject of reporting speech i.e. 'you' will be changed into 'we'.
Hence, option B is the correct answer.

This is a sentence of optative direct speech. Rules for changing such sentences into indirect narrations are given below:

• Said changes to prayed/wished/bade/cursed/thanked etc as per the sense of the sentence.
• Inverted commas (" ") are removed and “that” is used instead. However, in some sentences, “that” is not used.
• Reported speech (which has the verb and subject) is now written in the form of (subject + verb); reported speech is made assertive.
• If may is hidden, one can use may/might accordingly and the first form of verb is used with it.
• Sign of exclamation (!) if given is removed and full stop is used.
• The words like, this, these, tomorrow, yesterday change to that, those, the next day, the previous day respectively.

For sentences where "let us" is used in the reported verb, it should be changed to "suggested to or proposed to" in the indirect sentence. We can see that only option C satisfy this rule, so it is the correct answer.

This is a direct narration of exclamatory sentence. We change such sentences in indirect narration using following rules:

• Said is changes to exclaimed/exclaimed with joy/exclaimed with sorrow/ exclaimed with grief/ confessed with regret/ shouted with applause/ cried out/ eagerly wished as per the sense of the sentence.

• If the reporting verb is in present or future tense, no changes are made to the verb/tense of the reported speech. In such cases, says to changes to tells/comments.

• Inverted commas (" ") are removed and that is used instead.

• The verb and tense of the reported speech changes accordingly.

• Sign of exclamation (!) if given is removed and full stop is used.

• If the reported speech starts with "what a", then the word "very" in used in indirect narration and the sentence is made assertive.

The given sentence is in interrogative form. To convert such sentences into direct narration, the below rules are followed:

• Said/say is changed to ask/asked/wonder/wondered/enquire of/enquired of.
• Inverted commas (" ") are removed.
• If the reported speech is in YES/NO question form then if/whether is used before reported speech.
• If the reported speech is in the form of WH-Question (who/what/why/how/where/when/which etc), no conjunction is used before the question word. The question word itself works as a conjunction.
• Reported verb is made assertive; i.e. it is kept in the order of subject + verb.
• The sign of interrogation (?) is removed and full stop is used.
• The words like, this, these, tomorrow, yesterday change to that, those, the next day, the previous day respectively.

Hence, option C is the correct answer.