Final answer:
A fertilizer labelled 16:4:8 contains 16% nitrogen, 4% phosphorus (as P2O5), and 8% potassium (as K2O), which are key elements for plant growth.
Step-by-step explanation:
If a fertilizer is labelled 16:4:8, it indicates the percentage by weight of the three major nutrients essential for plant growth: nitrogen (N), phosphorus (P), and potassium (K), commonly referred to as NPK. The numbers on the fertilizer label represent the percentages of each of these elements in the form of nutrients that plants can absorb. Specifically, a 16:4:8 fertilizer has 16% nitrogen, 4% phosphorus (as P2O5), and 8% potassium (as K2O). While the phosphorus and potassium are not technically present as P2O5 and K2O, these designations are a conventional shorthand used for labelling.