Alpha decay emits a helium nucleus (2 protons, 2 neutrons)

Steps:

• Identify initial composition: 93 protons, 145 neutrons in neptunium-238.
• Recall alpha particle: 2 protons + 2 neutrons.
• Subtract from parent: new protons = 93 - 2 = 91; new neutrons = 145 - 2 = 143.
• Diagram must show both numbers decreasing by 2.

Why D is correct:

• D depicts protons and neutrons both reduced by 2, matching alpha emission definition.

Why the others are wrong:

• A: Shows only protons decreasing, ignoring neutron loss.
• B: Shows neutrons decreasing but protons unchanged, violating charge conservation.
• C: Shows increases in both, opposite of decay process.

Final answer: D