Which is a characteristic of the part of the atom marked
"A"?
A
It contains most of the mass.
It is negatively charged.
It is mostly empty space.
It is composed of electrons.
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The correct answer is "It contains most of the mass".

Explanation:

The part of the atom marked "A" belongs to the nucleus. The nucleus contains most of the mass of the atom, since the other part of the atom belongs to the electron and the mass of the electron represents only 1/1836 of the mass of the lightest nucleus. The nucleus of the atom is positive, since it is comprised of protons and neutrons, which are positive and neutral, respectively. The exception is the hydrogen's nucleus that is comprised of only one proton, but is positive as well. I attached the missing figure.

thats how its supposed to be

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