question #1
x=(...) 1011
y=(...) 1011 will also accept 0001 0001 (if you considered 011 as base 16)
z=(...) 0010 1100
z1=(...) 1000
z2=(...) 0011 1100

question #2
aa=1100 0101
ab=0001 0010
a =0000 1011
b =1010 1010
c =1010 1010
d = false