a decrease in the nominal money supply by the Federal Reserve, all
else constant, shifts the aggregate demand(AD) curve left, while a
decrease in the price level,all else constant, shifts the AD curve to
the right.

Is this statement right? why?

AD = C + I + G + X - M, where C=consumption, I=investment, G=govt
spending, X=exports, M=imports.

When money supply decreases, interest rates rise. Faced with higher
interest rates (money becomes more "expensive"), C and I falls. AD
thus falls (shifts to the left).