Normalization

Question

let R1 and R2 be relations α₂ is set of attributes of R2.let α2 is foreign key in R2, referring to α₁ of relation R1.

Consider the following points about above

1. α₂ is primary key of R2.

2.  α₁ is primary key of R1

3. α₂ may or may not be primary key of R2

4. α₁ may have null values

5. α₁ need not be key of R1

whichiof the above is true

a) 1 and 2

b) 1,4 and 5

c)2 and 3

d)2,3 and 4

Comments

what is source of question ??.
option 1 is wrong a foreign key may contain duplicate value hence 1 is wrong . and from bellow link it seems that option 2 is also wrong bcoz a foreign key can reffer to a primary or alternate key 
http://stackoverflow.com/questions/18435065/foreign-key-to-non-primary-key
  hence no option is matching.
i think option 3 is only correct.

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Source of the question

Answer 1

Frnds foreign key generally refers to only primary key(mentioned in every book)..so. And c is true.

Answer 2

1. Its not necessary that a foreign key has to be the primary key of a relation. Therefore 1 is FALSE

2. Every foreign key must be the Primary key of the foreign relation. Therefore 2 is TRUE.

3. if 1 is False this is automatically TRUE.

4. Since a1 is primary key therefore it cant have null values. Therefore FLASE.

5. Already stated that a1 is primary key of R1. 

Therefore option C i.e. 2 and 3 are TRUE.