Step 1: Understanding the Concept:
Mental health is defined as a state of emotional and psychological well-being in which a person can cope with normal stress and function positively. A mentally healthy child's everyday mood reflects this state.
Step 2: Why option A is correct.
A child in good mental health typically shows a stable, positive mood, adjusts well to their surroundings, and stays generally happy and cheerful in daily life.
Step 3: Why the other options are wrong.
Irritation, sadness, and loneliness are signs commonly linked to poor mental health, stress, or emotional difficulty, which is the opposite of what "mentally healthy" describes.
Final Answer:
A mentally healthy child remains happy. This corresponds to option (A).