Explain how calcium (40ca20) and flourine (19f9) became stable when they form calcium fluoride.

Calcium has two valence electrons and fluorine has space for one more electron  in order to complete its valence orbital, therefore one calcium atom combines with two fluorine atoms to form caf2.

Enzyme make a hormone as a catalyst

the catch is that the top numbers are atomic masses the bottom numbers are the numbers of protons and electrons in an uncharged atom. they are the number of that atoms as you would find them on the periodic table. further, the numbers on the left are used to determine the missing numbers on the right

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer