Higher order (>3) reactions are rare due to

The ionic radii (in Å) of N^3–, O^2– and F^– are respectively:

Which of the following is the energy of a possible excited state of hydrogen?

If the function.

$$g\left( x \right) = \left\{ {\matrix{ {k\sqrt {x + 1} ,} & {0 \le x \le 3} \cr {m\,x + 2,} & {3 < x \le 5} \cr } } \right.$$

is differentiable, then the value of $$k+m$$ is :