Intensity Unit from Energy, Time, and Area

Steps:

• Energy in SI is kg m² s^{-2} (joule).
• Intensity = energy / (time × area), so divide by s and m².
• This yields (kg m² s^{-2}) / (s × m²) = kg s^{-3}.
• Thus, base unit is kg s^{-3}.

Why D is correct:

• Matches definition: energy flux yields kg s^{-3} after canceling m² and one s.

Why the others are wrong:

• A: kg^{-1} s^{-1} inverts mass and lacks s^{-3} power.
• B: kg m^{-3} resembles density, ignores time factor.
• C: kg s^{-1} has insufficient negative time exponent (needs -3).

Final answer: D