Apotassium (k) atom attains a stable electron configuration when it combines with. one chlorine atom two chlorine atoms one calcium atom two calcium atoms

Answer is: one chlorine atom.
They form ionic compound potassium-chloride (KCl).
Electron configuration of potassium: ₁₉K 1s²2s²2p⁶3s²3p⁶4s¹.
Electron configuration of chlorine: ₁₇Cl 1s²2s²2p⁶3s²3p⁵.
Potassium lose one electron to attains a stable electron configuration of noble gas argon (Ar).

Elias is almost correct. he just got it backwards.the correct answer is that it demonstrates elastic potential energy transforming into kinetic energy.

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