Countable/uncountable noun?

[Leong187]

I learnt that when a word such as 'enthusiasm' is first modified by an adjective or modified by a relative clause in order to specify that it is a certain type of or a very special instance of that noun, then the indefinite article can sometimes be used.

What about the following sentences:

1) This dictionary is available in electronic form.
2) The car has been well maintained and is in excellent condition.
3) The house was in a terrible condition.

Some words are modified by an adjective, yet they are preceded by zero article. I am confused about the precise and correct usage of the articles.

[Beeesneees]

1) an electronic form/electronic form - both are acceptable
2)an excellent condition/excellent condition - both are acceptable
3) in a terrible condition - the article is required.
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Cheers m' dears!

[Leong187]

1) In what context do we use 'electronic form' and 'an electronic form'? Can they be used interchangeably?
2) In what context do we use 'in excellent condition' and 'in an excellent condition'? Can they be used interchangeably?
3) Is it ok to omit the article 'a'?

[Beeesneees]

1) They are interchangeable in the example.
2) They are interchangeable in the example.
3) No. The article is required.
_________________
Cheers m' dears!

[Leong187]

Why are they interchangeable in sentences (1) and (2) but not sentence (3)?

Thanks in advance.

[Beeesneees]

Sorry - on re-reading, it's possible to omit it there too - it's not as common though, so it threw me. I should have thought a little harder about the possibilities.
_________________
Cheers m' dears!