Total constructive interference occurs when two waves with similar frequency and wavelength:

Options:

1. have 90 degrees phase difference.

2. are completely out of phase.

3. have 45 degrees phase difference.

4. are completely in phase.

5. have a phase difference of - 90 degrees.

4.

Explanation:

If the waves have similar frequency and wavelength, this means that they will reach to their maximum amplitude approximately at the same time, at any given distance from the source, provided they have exactly the same phase.

Otherwise, the interference will not be totally constructive, decreasing the total amplitude as the phase increases, until reaching to a totally destructive interference when both waves are completely out of phase (180º difference).