The sides of safety matches contains:
a) Red phosphorous + sand powder
b) \[{\text{C}}{{\text{a}}_3}\left( {{\text{P}}{{\text{O}}_4}} \right) + {\text{glass pieces}}\]
c) \[{\text{C}}{{\text{a}}_3}\left( {{\text{P}}{{\text{O}}_4}} \right) + {\text{glass pieces}}\]
d) ${\text{KCl}}{{\text{O}}_3},{\text{KN}}{{\text{O}}_{3,}}{\text{Sulphur + Antimony}}$

Hint: If you’ve ever seen safety matches(or regular matchbox) and observed its carefully or even casually you might have seen what colour it has, now try to find that colour in the given mentioned.

Complete step by step solution:
The answer to the question is the option (a) i.e, red phosphorous and sand powder, If the mentioned hint was enough for you to figure out that then great, but if it was of no help well worry not we will look at how it is a correct answer.
First, let’s understand how a matchstick works,
The basic principle is friction but many other factors are involved than just friction. When the head of the matchstick( the red part) is rubbed with either side of the box it creates friction and friction produces heat which results in the following chemical reaction;
The red phosphorous gets converted to white phosphorous (because of the heat produced from friction)
Due to its high reactivity, the white phosphorous thus formed reacts with the potassium chlorate [ (${\text{KCl}}{{\text{O}}_3}$ ) present in the head to a matchstick]and produces more heat and ${{\text{O}}_2}$, this reaction can be understood as;
${\text{KCl}}{{\text{O}}_3} + {\text{ }}{{\text{P}}_4} \to {\text{ }}{{\text{O}}_2} + \Delta ({\text{Heat)}}$
This heat then reacts with antimony trisulfide (${\text{S}}{{\text{b}}_2}{{\text{S}}_3}$) and ignites it.
This ignition is continued due to the oxygen liberated from the reaction of white phosphorus and potassium chlorate.
Therefore we need the red P and sandpaper to start the chemical reactions.

Hence the correct option is (a).

Note: Reading questions carefully is important, as the given options also mention the chemicals present in the head of a matchstick, but the questions ask for what are the components present in the sides of a matchbox.