Answer:

Explanation:
Given that,
Wavelength, 
We need to find the frequency of the violet light.
We know that the relation between frequency and wavelength is given by :

So, the frequency of violet light is
.
What’s the question or problem ?
The light coming out of a concave lens will never meet.
So, the answer is A. will never meet.
Happy Studying! ^^
My opinion, the answer is b
Answer:
the hydrogen filled balloon is denser than the air filled balloon