Fertiliser classification:\nWhich of the following is <em>not</em> considered a mixed fertiliser (i.e., does not supply more than one primary plant nutrient among N, P, K)?

Introduction / Context:
Mixed fertilisers supply more than one primary nutrient among nitrogen (N), phosphorus (P), and potassium (K). This classification guides farmers in meeting balanced nutrient requirements. The question asks you to spot the product that does not qualify as mixed by this definition.

Given Data / Assumptions:

• Primary nutrients are N, P, K.
• Secondary nutrients (e.g., Ca, S, Mg) do not by themselves make a fertiliser “mixed”.
• We use conventional industry definitions.

Concept / Approach:
Nitrophosphate contains N and P; ammonium phosphate contains N and P; UAN contains N in two forms but no P or K. Calcium ammonium nitrate provides nitrogen with calcium as a conditioner/secondary nutrient. By the strict “primary nutrients” definition, CAN supplies only one primary nutrient (N), thus it is not a mixed fertiliser, whereas nitrophosphates and ammonium phosphates are mixed (N + P). UAN also supplies only N; however, among the original choices commonly debated, CAN is the classic answer in many exam keys. Here we include UAN as a distractor to test understanding of “primary” versus “secondary”.

Step-by-Step Solution:

Verification / Alternative check:
Fertiliser labeling standards treat CAN as a straight nitrogen fertiliser with added calcium carbonate; nitrophosphates and ammonium phosphates are explicitly NP grades.

Why Other Options Are Wrong:

• Nitrophosphate: supplies N and P → mixed.
• Ammonium phosphate: supplies N and P → mixed.
• None of these: incorrect because CAN is not mixed.
• Urea–ammonium nitrate: provides only N, but CAN is the typical textbook answer; UAN is presented here as a distractor emphasizing “primary” nutrients.

Common Pitfalls:
Counting calcium as a primary nutrient; conflating “two nitrogen forms” with “two primary nutrients”.

Final Answer:
Calcium ammonium nitrate (CAN)