What mostly determines the chemical properties of the atom of an element

the electrons i.e their valence electron

Explanation: valence electron is the number of electron in the outermost shell of an atom. Infact it is the combining power of an element. The valence electron gives us a better understanding of how an element will react with other elements. This is the reason why elements with the same number of valence electron(s) are grouped together telling us that they exhibit similar chemical properties

a: 45.9 meters

b: 4.29 seconds

step-by-step explanation:

a: h(t)=1/2(-9.8)(3)^2+0(3)+90

h(t)=-4.9(3)^2+90

h(t)=-44.1+90

h(t)=45.9 meters

b: 0=1/2(-9.8)(t^2)+0t+90

0=-4.9t^2+90

-90=-4.9t^2

18.37=t^2

t=4.29 seconds

in the second question, the numbers aren't exact, but they're a close approximation.