Answer:
D. fall by $100
Step-by-step explanation:
fall by $100
When fed sells $500 to commercial banks, banks keep 20% of deposit with themselves which is $100. Rest $400 will be loaned out in the economy. When fed buys $500 of securities, $500 is pulled out from the economy. Hence the total effect = $400 - $500 = - $100. Thus, in total there will be a fall in $100