Whos the first person to propose the concept of an atom?

Democritus

Explanation

He was a Greek philosopher who was the first person to use the term atom

Democritus

hope it's help you...

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