Which of the following is a scalar quantity?

Under which one of the following conditions do real gases approach the ideal gas behaviour?

$A$ man slides down a telegraphic pole with an acceleration equal to one-fourth of the acceleration due to gravity. The frictional force between the man and the pole is equal to which of the following in terms of the man's weight $w$?

If the direction cosines of two lines are given by $l+m+n=0$ and $l^2-5m^2+n^2=0$,then the angle between them is

Select the correct pair from the following.

$A$ bimetallic strip consists of metals $X$ and $Y$. It is mounted rigidly at the base as shown in the figure. The metal $X$ has a higher coefficient of linear expansion compared to that of metal $Y$. When the bimetallic strip is placed in a cold bath, what happens?