Q.Assign the CIP priority order to the four substituents on the stereocentre of $\text{CHFClBr}$ (bromochlorofluoromethane), and determine whether the isomer drawn with $\text{Br} \to \text{Cl} \to \text{F}$ appearing clockwise (with H pointing away from the viewer) is $R$ or $S$.

Since $\text{Br}$, $\text{Cl}$, $\text{F}$ and $\text{H}$ are all different elements directly attached to the stereocentre, CIP priority is fixed purely by their atomic numbers: bromine (35) outranks chlorine (17), which outranks fluorine (9), which outranks hydrogen (1) -- no need to look further out along any substituent. With the lowest-priority group, hydrogen, oriented away from the viewer as the CIP rule requires, tracing the remaining three groups in priority order $\text{Br} \to \text{Cl} \to \text{F}$: if this path runs clockwise, the centre is labelled $R$ (rectus); a co …

When all four attached atoms are different elements, priority is read straight off atomic number with no need for further comparison; only orient with the low …

Trying to trace the priority path without first mentally placing H away from the viewer -- if the lowest-priority group points toward the viewer instead, the apparent cloc …