Which of the following is correct about "Efficiency"?

The correct answer is option 4- All of the above.

OPTION 1-Focuses on optimum use of resources
OPTION 2-Involves cost benefit analysis
OPTION 3-Means doing the task correctly and with minimum cost

Efficiency means doing the task correctly and with minimum cost. There is a kind of cost-benefit analysis involved and the relationship between inputs and outputs. If by using less resources (i.e., the inputs) more benefits are derived (i.e., the outputs) then efficiency has increased. Efficiency is also increased when for the same benefit or outputs, fewer resources are used and less costs are incurred.
So, all the points are related to efficiency so the correct ans is all of these.