To determine the most suitable reagent for the conversion of $RCH_2OH \to RCHO$, we need to convert a primary alcohol to an aldehyde. The primary alcohol $RCH_2OH$ can be oxidized to an aldehyde $RCHO$.
The options given are:
$KMnO_4$
$K_2Cr_2O_7$
$CrO_3$
$PCC$ (pyridine chloro chromate)
To find the correct reagent, let's consider the oxidation capability of each reagent:
$KMnO_4$ is a strong oxidizing agent and tends to oxidize primary alcohols to carboxylic acids rather than stopping at the aldehyde stage.
$K_2Cr_2O_7$ is also a strong oxidizing agent typically used in acidic conditions, and it can convert primary alcohols directly to carboxylic acids.
$CrO_3$ is another strong oxidizing agent used in the Jones reagent. It also tends to oxidize primary alcohols directly to carboxylic acids.
$PCC$, or pyridine chloro chromate, is a moderately oxidizing reagent that can selectively oxidize primary alcohols to aldehydes without further oxidation to carboxylic acids.
Among these reagents, $PCC$ is the most suitable for selectively converting a primary alcohol to an aldehyde without over-oxidation. Therefore, the correct answer is $PCC$ (pyridine chloro chromate).
