In ΔABC, BD is the internal bisector of ∠B meeting AC at D. If CD = 7…

BD is bisector of angle B

In $\mathrm{△BDA}$ and $\mathrm{△BDC}$

$\mathrm{AB/BC\; =\; AD/CD\; =\; (AC-CD)/CD\; =\; (10.5-7)/7\; =\; 3.5/7\; =\; 1:2}$

$\mathrm{AB:BC\; =\; 1:2}$

The correct answer is Option (2) → 1 : 2