Answer
(a) The amplitude remains the same, and the
angular frequency increases.
Work Step by Step
Since zero velocity is not changed, it means amplitude is same. Now since mass is decreased time period will also decrease because mass and time period are directly related as
$T=2π\sqrt{\frac{m}{k}}$
Thus T will decrease resulting in increased angular frequency as
$\omega =\frac{2π}{T}$
