For the compositive table of a cyclic group shown below

Which one of the following choices is correct?

Which one of the following is TRUE for any simple connected undirected graph with more than $$2$$ vertices?

What is the chromatic number of an $$n$$-vertex simple connected graph which does not contain any odd length cycle? Assume $$n \ge 2$$.

$$\int\limits_0^{\pi /4} {\left( {1 - \tan x} \right)/\left( {1 + \tan x} \right)dx} $$ $$\,\,\,\,\,\,$$ evaluates to