To do or To be done

Question

Which of these are correct

1. This is easy to do

2. This is easy to be done

3. The question is easy to answer

4. The question is easy to be answered

5. That box is easy to carry

6. That box is easy to be carried

I have been really confused between the two usages and to me both seems to be correct but I am not sure. So could you please help me with understanding these and the reason or grammar rules behind it.

And how about these:

7. This question can be answered

8. I am waiting for the water to boil

9. I am waiting for the water to be boiled/get boiled

I would really be grateful if you could tell the reason for this one also.

Answer 1

While I agree with much of the answer by Jack O'Flaherty, I would say that example 3: "The question is easy to answer." is perfectly correct and idiomatic.

I would also say that example 6 "That box is easy to be carried" is not correct.

This results in all of the "to be verbed" examples being listed as incorrect, while all three "this thing is easy to verb" are correct.

The adverbial forms (using "easily") suggested in the other answer are also correct, but there is a very small difference in meaning.

Answer 2

I answered a similar question a few days ago:
ELL Stack Exchange "tough movement"

In your example, 1,3 and 5 are correct, as explained at the link. I think the passivized versions you ask about are ungrammatical, however, you could say directly,
2a. This is easily done.
4a. This question is easily answered.
6a. This box is easily carried.

(The original answer said 1, 5, and 6 were correct; 6 was never correct for the same reason as 2 and 4. Thanks to David Siegel's correct answer.)

Answer 3

grammar rules behind it.

What's happening is called "passive voice". Verbs in passive voice are expressed with {form of be} + {past participle}.

Passive voice is used when we don't know who is doing an action, don't care, or otherwise want to de-emphasize the "agent". Business contexts often use passive voice to emphasize "teamwork" over an individual's action, and contexts where we don't want to seem like we are placing blame are also common for passive voice use.
Who is doing an action is called an agent, and the agent, if known and desired to be expressed, can be specified with a by X.

I drove the car.

The car was driven by me.

Passive voice works with infinitives - so I want to walk my dog and I want my dog to be walked by me are valid.

Passive voice can be used when talking to someone to make it clear you don't expect the other party of the coversation is supposed to be doing something. That's what 2, 4, and 6 sound like--you're telling someone this, but you don't want create the impression that someone has to do anything.

9. I am waiting for the water to be boiled

Boil can mean for an object to be in the state of boiling (The water is boiling), or for someone to perform a process bring an object to the state of boiling (X boils the water). This sounds like you are waiting for someone else to boil some water. If you wanted to say you are waiting for the water itself to start boiling, you should say #8.