Answer & Solution
Answer: Option B
Solution:

$$\eqalign{
& {\text{Given,}} \cr
& \angle A = {30^ \circ } \cr
& \therefore \angle C = {60^ \circ } \cr
& \left( {\tan {{60}^ \circ } = \frac{{\sqrt 3 }}{1} = \frac{{AB}}{{BC}}} \right) \cr
& AB = \sqrt 3 ,\,BC = 1 \cr
& \therefore AC = \sqrt {A{B^2} + B{C^2}} \cr
& = \sqrt {\left( {{{\left( {\sqrt 3 } \right)}^2} + {{\left( 1 \right)}^2}} \right)} \cr
& = 2\,{\text{unit}} \cr
& 2\,{\text{unit}} = 10\,{\text{cm}} \cr
& 1\,{\text{unit}} = 5{\text{ cm}} \cr
& \boxed{AB = \sqrt 3 {\text{ unit}} = 5\sqrt 3 } \cr} $$