How many different stereoisomers are possible for the following compound?
$Cl-CH=CH-CH(Cl)-CH=CH-Cl$

$P$ and $Q$ are isomers of dicarboxylic acid $C_4H_4O_4$. Both decolorize $Br_2/H_2O$. On heating,$P$ forms a cyclic anhydride.
Upon treatment with dilute alkaline $KMnO_4$,$P$ as well as $Q$ could produce one or more than one from $S$,$T$,and $U$.
$1.$ Compounds formed from $P$ and $Q$ are,respectively:
$(A)$ Optically active $S$ and optically active pair $(T, U)$
$(B)$ Optically inactive $S$ and optically inactive pair $(T, U)$
$(C)$ Optically active pair $(T, U)$ and optically active $S$
$(D)$ Optically inactive pair $(T, U)$ and optically inactive $S$
$2.$ In the following reaction sequences,$V$ and $W$ are respectively:
Give the answer for question $1$ and $2$.

Which is the correct structure of $D$-glyceraldehyde?

Total number of stereoisomers possible for the given structure:

How many chiral centers are in the following compound?

Calculate the total number of stereoisomers for the given molecule,considering the alkene configuration is fixed as trans.