sound of high frequency can be obtained when the wires of a violin are (longer/ shorter).

Shorter strings have higher frequency and therefore higher pitch. ... Tension refers to how tightly the string is stretched. Tightening the string gives it a higher frequency while loosening it lowers the frequency. When string players tighten or loosen their strings, they are altering the pitches to make them in tune.

number 2 is your answer.