Let $f(x)$ be the continuous probability density function of a random variable $x$, the probability that $a < x \leq b$, is :
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(B) f(b)−f(a) is not CDF.
Reason: Here function f is pdf not cdf.
Note: If X is Discrete RV then P(a≤X≤b) = F(b) - F(a) ,where F is CDF .Both f and F are diffrent.
@Akash Kanase and @Kapil I think selected answer requires small correction.