The number of possible isomers for butene $(C_4H_8)$ is..........

Which of the following reaction$(s)$ give$(s)$ a meso-compound as the main product?

Which of the following shows keto-enol isomerism?

The following molecule is fluorometholone,a steroidal anti-inflammatory agent. How many stereogenic centers does it contain?

Which of the following statements is $NOT$ correct?

$A$ 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?