Which represents the correct equilibrium constant expression for the reaction below? Upper C u (s) plus 2 upper A g superscript plus (a q) double-headed arrow upper C u superscript 2 plus (a q) plus 2 upper A g (s). K e q equals StartFraction StartBracket upper C u EndBracket StartBracket upper A g superscript plus EndBracket superscript 2 over StartBracket upper C us superscript 2 plus EndBracket StartBracket upper A g EndBracket superscript 2 EndFraction. K e q equals StartFraction StartBracket upper C u superscript 2 plus EndBracket StartBracket upper A g EndBracket superscript 2 over StartBracket upper C u EndBracket StartBracket upper A g superscript plus EndBracket superscript 2 EndFraction. K e q equals StartFraction StartBracket upper A g superscript plus EndBracket superscript 2 over StartBracket upper C u superscript 2 plus EndBracket EndFraction. K e q equals StartFraction StartBracket upper C u superscript 2 plus EndBracket over StartBracket upper A g superscript plus EndBracket superscript 2 EndFraction.