`{:(,,2NO_((g)),+,Br_(2(g)),hArr,2NOBr_((g))),(,"Initial mole",0.0870,,0.0437,,-),(,"Equilibrium",(0.087-2a),,(0.0437-a),,2a):}`
Given: `2a=0.0518`
`:. a=0.0259`
At equilibrium, `NO=0.0870-0.0518`
`=0.0352 "mole"`
`:. Br_(2)=0.0437-0.0259=0.0178 "mole"`