Why is the inside portion of the optical instruments like camera, telescope etc. made black?

Why are hydrocarbons insoluble in water but highly soluble in solvents like petroleum ether, benzene, carbon tetrachloride etc ?

Careful measurement of the electric field at the surface of a black box indicates that the net outward flux through the surface of the box is 8.0 xx 10^(3)N*m^(2)*C^(-1) . (a) What is the net charge inside the box? (b) If the net outward flux through the surface of the box where zero, could you conclude that there where no charges inside the box? Why or why not ?

In the earth's atmosphere ,light gases like hydrogen, helium, etc., are scarce- explain why.

Careful measurement of the electric field at the surface of a black box indicates that the net outward flux through the surface ofthe box is 8.0x10^3Nm^2//C . If the net outward flux through the surface of the box were zero, could you conclude that there were nd charges inside the box ? Why or why not ?

Optical and radio telescopes are built on ground but X-rays astronomy is possible only from satellites orbiting the earth. Why?