$3 \mathrm{~A} \rightarrow \mathrm{~B}, \mathrm{~K}_{\mathrm{c}}=4$$[\mathrm{A}]=0.5,[\mathrm{~B}]=\text { ? }$

$1.3 \times 10^{-9} \mathrm{~g}$

$1.366 \times 10^{-3} \mathrm{~g}$

$1.366 \times 10^{-7} \mathrm{~g}$

$1.366 \times 10^{-4} \mathrm{~g}$