Identify the conformer of $2$-methylpentane.

Which of the following compounds is achiral?

Which of the following compounds can exist in two different stereoisomeric forms?

When isomers have the same structural formula but differ in the relative arrangement of atoms or groups,they are called ........

$A$ compound was synthesized by a student,but its structure was not identified. However,his instructor told him that it was a meso compound with $5$ carbons and $2$ stereogenic centers. Which of the following structures should the student consider as possibilities for his compound?

The method of preparing an optically active substance from a symmetric molecule in the presence of an optically active substance is called .....