Bow is to Violin as Plectrum is to 

USA : Congress :: Iran : ? 

Direction : In the following question, select the related word form the given alternatives.
Coconut : Shell :: Letter : ?

Pea-hen : Pea - cock :: Bitch : ? 

Select the option that is related to the sixth number in the same way as the first number is related to the second number and the third number is related to the fourth number.
34 : 12 :: 28 : 16 :: ? : 15

F : 216 :: L : ? 

Choose the odd word/letters/number/number pair from the given alternatives. 

Given set
10, 12, 15