A cumulative distribution function \( F(x) = P(X \leq x) \) always has three guaranteed properties no matter what the underlying random variable is: it never decreases as \( x \) increases, it goes from \( 0 \) at \( -\infty \) to \( 1 \) at \( +\infty \), and the probability of landing in an interval is just the difference \( F(b) - F(a) \). Options (A), (B) and (C) are simply restating these three universal facts, so they always hold true for every distribution. The odd one out is option (D), which claims \( F(1) = \frac{1}{2} \) for every random variable. That cannot be a general rule since \( F(1) \) clearly depends on which distribution we are talking about. For example, for a random variable uniform on \( [0,10] \), \( F(1) = 0.1 \), and for an exponential random variable with rate \( 1 \), \( F(1) = 1 - e^{-1} \approx 0.632 \), neither of which is \( 0.5 \). So option (D) is not a property that holds in general, which makes it the answer to "which is not a property."