For most substances, the representative particle, or smallest unit in which the substance naturally exists, is the HELP

Three cards with holes are arranged in a straight line. a light is shined through the first card’s hole and travels through all three cards. what does this tell you about light rays? a) that light is reflected b) that light is refractive c) that light travels in a straight line d) that light does not travel in a straight line

All of the following are part of the biosphere except

Name the element in group 17, period 2. (periodic table)