If f(x) \( = \left\{ {\begin{array}{*{20}{c}} {\rm x;if\;x\;is\;rational}\\ { \rm- x;if\;x\;is\;irrational} \end{array}} \right.\), then which of the following statement is not true:
1
f(x) is an odd function
2
f(x) is continuous at \(x = \frac 1 2\)
3
f(x) is continuous at x = 0
4
f(x) is a periodic function