A biologist studying the genetic code is interested to know the number of possible arrangements of 12 molecules in a chain. The chain contains 4 different molecules represented by the initials A(for a Adenine), C (for Cytosine), G (for Guanine) and T (for Thymine) and 3 molecules of each kind. How many different such arrangements are possible?

Assuming that each has icosahedral strcucture, determine how many isomers are possible for the B_(10) C_(2) H_(12) molecule ?

A cylinder contains 32 g of methane gas at S.T.P. How many molecules of ammonia are present in the cylinder ? [C-12, H-1]

A schematic analysis of the reaction of the enantiomer with racemic mixture is shows below: {:(d,+,"d and l",rarr,(d)-(d)),("The(+)-form of",,"A racemic mixture of",,+),("chiral molecules",,"other molecules with",,(d)-(l)),(,,50%(d) and 50%(l),,):} The products (d-d) and (d-l) are clearly neither identical nor enantiomers (non-superimposable mirror images) as the diastereomers, stereoisomers that are not mirror images' . The formation of diasteromers allows the separation of enantiomers (called resolution) which is not easy as enantiomers have identical physical properties. One general with naturally occurring chiral molecule to form a pair of diastereomers. These can be separated easily as they have different physical properties. If the original chemical reaction can be reversed, the enantiomers can be isolated. How many diastereomers are possible among all the possible stereoisomers of 2,3-dibromopentane ?