A ladder is resting on a smooth ground and leaning against a rough vertical wall. The force of friction will act

zero at its upper end

A ladder is resting on a rough ground and leaning against a smooth vertical wall. The force of friction will act zero at its upper end.

less than

In a screw jack, the effort required to lower the load is less than the effort required to raise the same load.

100 percent

An ideal machine is that in which there is no dissipation of energy in any manner. In an ideal machine, the work output is equal to the work input, i.e., efficiency of an ideal machine is 100%.
In ideal machines mechanical advantage is equal to velocity ratio.

load lifted to the effort applied

the mechanical advantage of a lifting machine is the ratio of load lifted to the effort applied.