what do you mean by brisk effervescence?

Are hydrogen and co2, both odourless and colourless gas?

which gas shows brisk effervescence?

Brisk effervescence is the fast or rapid evolution of a gas from a solution resulting in the formation of tiny bubbles on the surface of the solution. 
Yes, both hydrogen and carbondioxide gases are colourless and odourless.

Both the gases show brisk effervescence.