Need serious hep no JOKE so plz help me List the % by mass for each element:
First, add the total mass of 4 atoms of hydrogen, plus 2 atoms of carbon, plus 2 atoms of oxygen. Total mass = . To obtain percent by mass, divide the mass of each element by the mass of the total:

H=
C=
O=

The atomic radius of sodium is 186 pm and of chlorine is 100 pm. the ionic radius for na+ is 102 pm and for cl– is 181 pm. in going from na to cl in period 3, why does the atomic radius decrease while the ionic radius increases? a. the inner electrons in the sodium cation shield its valence electrons more effectively than the inner electrons in the chloride anion do. b. the inner electrons shield the valence electrons more effectively in the chlorine atom than in the chloride anion. c. the outermost electrons in chloride experience a smaller effective nuclear charge than those in the sodium cation do. d. the outermost electrons in chloride experience a larger effective nuclear charge than those in the sodium cation do. e. monatomic ions are bigger than the atoms from which they are formed.

Asap! will give brainiest when a heat wave strikes a region causing more people to run air-conditioning units, electrical demand increases. what needs to be done to meet this increased demand? raising the control rodslowering the control rodsremoving the control rods

How can the periodic table be used to predict the behavior of elements?