Answer:
a. 4KCN
Step-by-step explanation:
Four is a coefficient found in the chemical formula 4KCN.
KCN is potassium cyanides.
A coefficient is a number that is written before a chemical compound. It is usually used to balanced reaction expression.
Chemically such numbers indicate the number of moles or volume of that specie.
Since KCN is the only compound with 4 before it, so, the solution is KCN