Which of the following is least likely to behave as a Lewis base?

Which of the following is a favourable factor for cation formation?

If in a $\triangle ABC$,$r_1 < r_2 < r_3$,then:

If $f(t) = \int_{-t}^t \frac{e^{-|x|}}{2} dx$,then $\lim_{t \rightarrow \infty} f(t)$ is equal to:

The differential equation of the family of parabolas with the focus at the origin and the axis along the $X$-axis is:

The equilibrium constant for the given reaction is $100$.
$N_{2(g)} + 2 O_{2(g)} \rightleftharpoons 2 NO_{2(g)}$
What is the equilibrium constant for the reaction given below?
$NO_{2(g)} \rightleftharpoons \frac{1}{2} N_{2(g)} + O_{2(g)}$