Svarene er lette å skille.

Svarene is the definite plural form of svar, which means answer.

• et svar = an answer
• svaret = the answer
• svar = answers
• svarene = the answers

So the sentence is talking about the answers, not just answers in general.

Because lette has to agree with svarene, which is plural.

The adjective lett changes form depending on the noun:

• lett for singular neuter or as a general predicate in some cases
• lette for plural

Here, svarene is plural, so Norwegian uses lette:

• Svaret er lett å skille. = The answer is easy to distinguish.
• Svarene er lette å skille. = The answers are easy to distinguish.

Here it means easy.

The adjective lett can mean both:

• light in weight
• easy in difficulty

In this sentence, the meaning is clearly easy, because å skille is an action, so lette å skille means easy to distinguish / easy to tell apart.

Here å skille means to distinguish, to tell apart, or sometimes to separate, depending on context.

In this sentence, the natural meaning is to distinguish or to tell apart.

So Svarene er lette å skille means that the answers are easy to recognize as different from one another, or easy to tell apart.

Norwegian often leaves that idea understood when the context is clear.

So Svarene er lette å skille can naturally mean The answers are easy to tell apart, even though Norwegian does not explicitly say from each other.

If you want to make it more explicit, you can say:

Svarene er lette å skille fra hverandre.

That more clearly means The answers are easy to tell apart from each other.

Norwegian often uses an active infinitive after adjectives like lett and vanskelig, even when English would translate it with a more passive idea.

So:

• Svarene er lette å skille
  literally looks like The answers are easy to distinguish

but the real sense is:

• The answers are easy to distinguish
• The answers are easy to tell apart

You can also make the passive meaning more explicit in another structure:

Svarene kan lett skilles.
= The answers can easily be distinguished.

Both are natural, but lette å skille is a very common pattern.

Yes. The pattern [noun] + er + lett/lette + å + infinitive is very common.

Examples:

• Boken er lett å lese. = The book is easy to read.
• Spørsmålene er lette å forstå. = The questions are easy to understand.
• Svarene er lette å skille. = The answers are easy to distinguish.

This is a very useful pattern to learn, because it works much like English easy to + verb.

Yes, sometimes, but lette sounds more natural in this kind of sentence.

• lette å skille = easy to distinguish
• enkle å skille = simple to distinguish

Both can work, but lett/lette å + infinitive is the standard, everyday way to say that something is easy to do.

So Svarene er lette å skille is the more idiomatic choice.