Question

What is the ratio of the velocity of sound in hydrogen to the velocity of sound in oxygen?!?

Answer 1

hydrogen = 2/3
oxygen = 1/3

Assuming you're talking about the speed of sound in water

Answer 2

What has this to do with water?

The ratio of the 2 velocities is given by
\[\frac{ SpeedHydrogen }{ SpeedOxygen }\]

I certainly don't know those speed without looking them up, and I doubt whether anyone else her does.

SO
Look up the speeds in your text or on google
Insert them into the above formula and calculate the result

Answer 3

For an ideal gas, velocity is:

\(v=\sqrt{\Large\frac{\gamma RT}{M}}\)

Hydrogen and oxygen have the same \(\gamma\), because both are diatomic molecules, but have different molar masses.

Answer 4

Using Vincent's formula I have come up with a number which is very close to the value derived from my formula and a list od speeds of sounds in gases.
http://www.engineeringtoolbox.com/speed-sound-gases-d_1160.html