First property assures that probability density function of random variable x obtain the non-negative values at all times. From the shape of the probability density function curve it’s obvious that pdf, f (x) decreases as the random variable value goes away from the mean, µ. Likewise, probability density function f (x) increases as the random variable value gets closer to the mean, µ. Second property identifies that the area under the probability density function f (x) always equivalent to 1 in the definition interval of the random variable X. Third property suggests that normal distribution curve has a similar shape on both sides of the mean x=µ. That property also proposes the fact that, P (X < µ ) = P (X > µ ) =0.5. Fourth property indicates that the tails of the probability function goes to infinity and at no time crosses or touches the x axis.