The oxidation state of K2Cr2O7 is +6. option A,C,D are the oxidation state of other elements like O7,C14, etc.
+2+2x+(−2×7)=0+2 + 2x + (-2 \times 7) = 0+2+2x+(−2×7)=0
2x=122x = 122x=12
x=+6x = +6x=+6
