Some function (#) is defined for all numbers \(a\) and \(b\) as \(a\#b= a + b - ab\).

Now, since given that \(a\#b=0\), then \(a + b - ab=0\);

Express a in terms of b: \(a=\frac{b}{b-1}\)

If \(b=1\) then the given expression is undefined so \(b\) cannot equal to 1.

Answer: B.

Or:

\(a + b - ab=0\);

\((a-1)(1-b)+1=0\);

\((a-1)(1-b)=-1\).

If \(b=1\), then \((a-1)(1-b)=0\) not -1, so \(b\) cannot equal to 1.

Answer: B.