Which of the following compounds is not chiral?

(1) 1-chloropentane

(2) 3-chloro-2-methyl pentane

(3) 1-chloro -2-methyl pentane

(4) 2-chloropentane

'x' gm of a compound A3B2C5 contains 'y' gm of A atoms

 

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how to represent the possible fischer projections for 2-bromohexane