Fill in the blanks:
$(i)$ If a liquid sticks to the glass,the angle of contact for the liquid-glass interface will be ....... (acute / obtuse).
$(ii)$ The angle of contact between mercury and glass is .......... (acute / obtuse).

(A) $(i)$ When a liquid wets a solid surface (sticks to it),the adhesive forces between the liquid and solid molecules are stronger than the cohesive forces between the liquid molecules. This results in a concave meniscus,which corresponds to an acute angle of contact (less than $90^{\circ}$).
$(ii)$ Mercury does not wet glass because the cohesive forces between mercury atoms are much stronger than the adhesive forces between mercury and glass. This results in a convex meniscus,which corresponds to an obtuse angle of contact (greater than $90^{\circ}$,typically around $135^{\circ}-140^{\circ}$).