Which of the following tend to react by gaining 1 electron

Option (c) is the correct answer. Halogens react by gaining one electron.

The halogens in the periodic table are Florine, chlorine, Bromine, iodine, astatine

All these electrons are short of one electron in the outermost shell. so these halogens gain one electrons and form anions.

For example, Florine has an atomic number of 9. so its electronic configuration is given by 2,7. it needs one electron to complete its octet as

F + e> F⁻

All other halogens similarly gain one electron to react.

luster is not a good characteristic to use by itself because luster is the property of minerals that indicates how much the surface of a mineral reflects light. the luster of a mineral is affected by the brilliance of the light used to observe the mineral surface.