The set consist of numbers 0 and 1 so if we use any combination of those 2 numbers under some operation and get as result one of those 2 numbers that means set is closed under that operation.
for multiplication you get:
00 = 0
0 1 = 0
1 * 1 = 1
so all combinations used and answers are 0 and 1 which means set is closed under multiplication
It isnt for subtraction and addition because:
0-1 = -1
and 1 + 1 = 2
