if an ox extracts only 50% of potential energy in grass and out of this if the ox used 40% to build up its body ,then the overall efficiency of grass to become part of ox would be:

A)10% C)20%
B)15% D)30%

To find the overall efficiency of grass becoming a part of an ox, we need to multiply the efficiencies of each step.

Step 1: The ox extracts 50% of the potential energy in the grass.
Step 2: Out of this energy, 40% is used to build up the ox's body.

To calculate the overall efficiency, we multiply the efficiencies of each step:

Step 1 efficiency = 50% = 0.5
Step 2 efficiency = 40% = 0.4

Overall efficiency = Step 1 efficiency * Step 2 efficiency
= 0.5 * 0.4
= 0.2

Therefore, the overall efficiency of grass becoming a part of the ox is 20% (option C).