Which of the following is not a valid expression of Boolean algebra?

A)
~x + (y·~z) + x + ~y = 1
Since ~x + x = 1, the whole expression becomes 1. ✅ Valid

B)
x·~y + ~x·y + ~x·~y = 1
Factor:
~x·y + ~x·~y = ~x(y + ~y) = ~x
So expression becomes:
x·~y + ~x
This is not always 1. ❌ Not valid

C)
~(x + y + z) = ~x·~y·~z
This is De Morgan’s law. ✅ Valid

D)
x·~y + ~x·y + x·y = x + y
LHS simplifies to x + y. ✅ Valid