Stereochemistry

Step 1: Understanding optical isomerism.
Optical isomerism arises due to the presence of chiral (asymmetric) carbon atoms. The number of optical isomers for a compound is given by the formula , where is the number of chiral centers.

Step 2: Applying the formula.
For a compound with 3 asymmetric carbon atoms, the number of optical isomers is .

Step 3: Conclusion.
The correct answer is (B) 8, as it corresponds to the formula for calculating the number of optical isomers.

Step 1: Formula for atomic mass.
For a bcc structure, the relationship between the edge length , density , and atomic mass is given by: Where: - is the edge length of the unit cell, - is the density, - is Avogadro’s number, - is the number of atoms per unit cell for bcc structure.

Step 2: Calculation.
Substitute the values into the formula:
Step 3: Conclusion.
The atomic mass of the element is (A) 51.78.

Step 1: Recall condition for optical activity.
A compound is optically active if it contains at least one chiral carbon atom bonded to four different groups.

Step 2: Analyse 2-chloropentane.
In 2-chloropentane, the second carbon is attached to:
–
–
–
–
These four groups are different, making it a chiral center.

Step 3: Analyse other options.
3-Chloropentane: Has two identical ethyl groups → achiral.
2-Chloropropane: Has two identical methyl groups → achiral.
2-Chloro-2-methylbutane: Central carbon has identical alkyl groups → achiral.

Step 4: Conclusion.
2-Chloropentane is optically active due to the presence of a chiral carbon.

Step 1: Recall formula for optical isomers.
Maximum number of optical isomers is given by: where is the number of asymmetric carbon atoms.
Step 2: Substitute given value.
Step 3: Conclusion.
Therefore, 16 optical isomers are possible.