What is formed when $cis-2-butene$ is reacted with cold dilute $KMnO_4$?

Propene on treatment with $HBr$ gives

Compound $X$ on reaction with $O_{3}$ followed by $Zn/H_{2}O$ gives formaldehyde and $2-$methylpropanal as products. The compound $X$ is :

Reagent $A$ may be:

For the synthesis of $but-1-ene$,$CH_3MgI$ should be treated with:

Some addition reactions of alkene are given below. Identify the one which fits on $ALL$ the given criteria.
Reaction must have-
$(A)$ Stereochemistry of addition - $SYN$ $ONLY$
$(B)$ Regiochemistry of addition - $ANTI-MARKOVNIKOV$ $OR$ $ANTI-MARKOVNIKOV$ $LIKE$