The number of circles that touch all the three lines $x+y-1=0$,$x-y-1=0$,and $y+1=0$ is

Which one of the following gases can deplete the ozone layer in the upper atmosphere?

In an astronomical telescope in normal adjustment,a straight black line of length $L$ is drawn on the objective lens. The eyepiece forms a real image of this line. The length of this image is $l$. The magnification of the telescope is

The radiant energy from the sun incident normally at the surface of the earth is $20 \ kcal/m^2-min$. What would have been the radiant energy incident normally on the earth if the sun had a temperature twice of the present one? (in $kcal/m^2-min$)

Which of the following equations represents a circle?

The number of nodal planes in a $p_x$ orbital is