Assume under APT, the stock returns are exposed to one macro factor, F$.$ Given the following information, does an arbitrage opportunity exist? If so$,$ what is the net gain of the arbitrage?

$\backslash$table$[[,$Expected Return,Beta on the Macro Factor F$],[$Stock A$,10\%,1],[$Stock B$,5\%,0\mathrm{.}5],[$Risk$-$free Instrument,$2\%,0]]$

An arbitrage opportunity exists; net gain $2\%$

No arbitrage opportunity exists

An arbitrage opportunity exists; net gain $5\%$

An arbitrage opportunity exists; net gain $1\%$