Which one of the following pairs represents stereoisomerism?

The compounds $(X)$ and $(Y)$ are formed by replacing $H_a$ with $D$ (while keeping $H_b$ as $H$) and replacing $H_b$ with $D$ (while keeping $H_a$ as $H$) respectively in the given molecule. What is the relationship between $(X)$ and $(Y)$?

Identify the total number of compounds containing at least one chiral carbon atom from the following list:
$1$. $2-$methylcyclohexanone
$2$. Cyclopentane$-1,3-$dione
$3$. $CH_3-CH_2-CH(NO_2)-COOH$
$4$. $CH_3-CH(I)-CH_2-NO_2$
$5$. $CH_3-CH_2-CH(OH)-CH_2OH$
$6$. $CH_3-CH_2-CH(I)-C_2H_5$

Arrange the following compounds in decreasing order of their acidic strength:

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

$A$ pair of stereoisomers might be classified in various ways. Which of the following statements are true with respect to pairs of stereoisomers?
$a$. They might be configurational isomers
$b$. They might be diastereomers
$c$. They might be constitutional isomers
$d$. They might be tautomers
$e$. They might be conformational isomers
$f$. They might be enantiomers
$g$. They might be positional isomers