I believe it is C. as liquid hydrogen.
The solution to this is to use the n = c / v equation
Where:
c is the speed of light: 3x10^8; and
The idea that v = m/s
So plug in the m/s for v in the n = c v equation and you will
get:
1.5 = (3 x 10 ^ 8)/ ((4.5m)/s))
Therefore, the time should be 2.25 x 10 ^ -10 seconds.
