Answer:

So then our answer would be:
D. 7.50 × 10¹⁴Hz
Step-by-step explanation:
For this case we know the frequency for the blue light, given by the problem:

We can convert this into m like this:

We know that the speed of light is a constant and is given by:

And assuming that we have a fundamental wave, we need to satisfy the following basic relationship:

And if we solve for the frequency from the last formula we got:

Now if we replace the values given we have:

So then our answer would be:
D. 7.50 × 10¹⁴Hz