1. i: The imaginary unit, which is defined as the square root of -1. 2. 2i: A multiple of the imaginary unit. 3. -3i: A negative multiple of the imaginary unit. 4. 4 + 5i: A complex number with a real part (4) and an imaginary part (5i). 5. -2 - 7i: A complex number with a negative real part (-2) and a negative imaginary part (-7i). 6. 3i^2: The square of the imaginary unit, which equals -3. 7. (2 + i)(3 - 4i): The product of two complex numbers, resulting in a complex number with both real and imaginary parts.