A CPU has 24-bit instructions. A program starts at address 300 (in decimal).…

Key insight: a 24-bit instruction occupies 3 bytes, so instruction addresses must lie on 3-byte boundaries.

• Start address is 300, so valid instruction addresses are 300 + 3n for integer n ≥ 0.

• Check each candidate address:

• 400: 400 mod 3 = 1 → not an instruction boundary

• 500: 500 mod 3 = 2 → not an instruction boundary

• 600: 600 mod 3 = 0 → is an instruction boundary (600 = 300 + 100*3)

• 700: 700 mod 3 = 1 → not an instruction boundary

Therefore, 600 is the legal program counter value because it lies on the required 3-byte instruction boundary.