Which of these parts of a reflecting telescope is used to gather and focus light?

a. lens

b. tube

c. convex mirror

d. concave mirror

Option (B), (C) and (D)

Explanation: In a reflecting telescope, concave and convex mirrors are used to focus light, in a tube.

In case of a reflecting telescope, a concave mirror is usually placed at one end of the telescope's tube whereas the other end is kept open from where the light is allowed to pass through. In between this two end of the tube, a comparatively small flat mirror is used, placing it at an angle of approximately 45°, that further reflects the reflected light to the eyepiece containing a convex mirror where a large image is observed.

Thus the above mentioned options (B), (C) and (D) are used in a reflecting telescope.

the ideal gas law equation is as follows

pv = nrt

where p - pressure

v - volume

n - number of moles

r - universal gas constant

t - temperature

so if the pressure, volume and temperature are already known

we are left with n and r

since r is the universal gas constant that has a known fixed value then r too is known

so we are left with 'n'

once we know temperature volume and pressure

we can find the number of moles of gas present using the ideal gas law equation

this is not my own answer, this is an answer for the same question by the user blahblahmali. i do not claim ownership of this account.