Two stove 'A' and 'B' were used by different person. 'A' produce yellow flame and 'B' produce blue flame. Which burner is needed to clean and why?

The yellow flame. Yellow light is an indicator that the temperature is low which implies incomplete energy conversion, incomplete combustion or way too much air intake. Given that burners are physically constrained not to run lean, it is a safe assumption to conclude it is overly rich due to plugging of some sort. Clean the yellow one.

Edited December 30, 201014 yr by cypress

The ideal bunsen burner flame should look like the one pictured on the left.

 

 

Two distinct cones, both blue but one really bright.