Which best describes eras and periods? Eras have a smaller time span than periods. Eras and periods are independent of each other. Eras and periods both appear at the start of the Cambrian period. Eras were more recently established on the time scale than periods.

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

Matter- occupies space and possesses rest massno matter is the opposite

In any atom of any element, you will find protons and neutrons in the nucleus of any atom 

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