Question

2. Collocations sound "right" to native English speakers
because they
sound unnatural
rarely used
are often used
are

Answer 1

collocations sound "right" to native English speakers because they are often used

Answer 2

'Are often used' is the answer.

About collocations:

• Collocation means the usage of two or more words together.
• That is people use two or more words joined often and use them commonly and casually.
• Sometimes, the collocations may not be right, still it is practised by people because they use them regularly and find no mistake in these at all.
• Moreover collocations come to practice when the native speakers speak them.
• For example, it must be 'heavy rainfall'. But now a days we see collocations like 'strong rainfall' readily accepted.
• Therefore collocations sound "right" to native English speakers because they are often used.