Which of the following pairs is/are correctly matched?

Reaction	Product
$I$. $RX + AgCN$	$RNC$
$II$. $RX + KCN$	$RCN$
$III$. $RX + KNO_2$	$RONO$
$IV$. $RX + AgNO_2$	$RNO_2$

The transition state of the given $S_N2$ reaction is:

Consider the $S_N1$ solvolysis of the following halides in aqueous formic acid:
$(I)$ $CH_3-CH(CH_3)-CH(Br)-CH_3$
$(II)$ $CH_3-C(CH_3)(Br)-CH_3$
$(III)$ $C_6H_5-CH(Br)-C_6H_5$
$(IV)$ $C_6H_5-CH(Br)-CH_3$
Which one of the following is the correct sequence of the halides given above in the decreasing order of their reactivity?

An organic compound $A$ $(C_4H_9Cl)$ on reaction with $Na$/dry ether gives a hydrocarbon which on monochlorination gives only one chloro derivative. What is $A$?

The major product of the reaction is:

For the given reaction
$R_1-C(R)(X)-R_2 \xrightarrow{HOH} R_1-C(R)(OH)-R_2$
Which substrate will give maximum racemisation?