statistics Questions

Consider the following statements:
(a) Mode can be computed from histogram
(b) Median is not independent of change of scale
(c) Variance is independent of change of origin and scale.
Which of these is/are correct?

In a series of $2n$ observations, half of them equal $a$ and remaining half equal $-a.$ If the standard deviation of the observations is $2,$ then $|a|$ equals