Why does the first row in our periodic table only have two elements?

A) because each orbital in every sub-level only holds
two electrons

B) because Bohr only knew about two elements

C) because the first energy level only holds two
electrons total
Help me pl

Astudent is given an assignment to demonstrate diffraction. he takes a photograph of a straw in a glass of water. the straw appears bent at the water level. which best describes this example? a) this is a good example of diffraction. b) this is an example of dispersion and not diffraction. c) this is an example of refraction and not diffraction. d) this is an example of reflection and not diffraction.

Aquarterback pedals 3.3meters southward and then run 5.7meters northward. whats the distance ? and whats the displacement?

Iwill give 30 points to whoever answers ! what is the formula for actual mechanical advantage and ideal mechanical advantage?