Can someone help? thx

Give one example to show that when substances are mixed, it may result in a chemical or a physical change depending on the conditions.

What do the atoms of elements in the same group have in common? a. they have the same atomic numbers. b. they have the same average atomic masses. c. they have the same number of electron shells. d. they have the same number of electrons in their outermost shells.

Two solutions of the same uv-absorbing molecule were analyzed by uv-vis spectroscopy on the same instrument using 1 cm pathlength cells. use data from the table to calculate by what percentage the concentration of solution b is compared to that of solution a. sample absorbance at 315nm a 0.45 b 0.80