Which of the following is not a Lewis acid?

If $S_{n} = 1^3 + 2^3 + \ldots + n^3$ and $T_{n} = 1 + 2 + \ldots + n$,then

Which of the following statements are true about acceleration due to gravity?
$(a)$ $g$ decreases in moving away from the centre if $r > R$
$(b)$ $g$ decreases in moving away from the centre if $r < R$
$(c)$ $g$ is zero at the centre of the Earth
$(d)$ $g$ decreases if the Earth stops rotating on its axis

If the coefficients $a$ and $b$ of a quadratic expression $x^2+ax+b$ are chosen from the sets $A=\{3,4,5\}$ and $B=\{1,2,3,4\}$ respectively,then the probability that the equation $x^2+ax+b=0$ has real roots is

In the study of a transistor as an amplifier,if $\alpha = \frac{I_C}{I_E}$ and $\beta = \frac{I_C}{I_B}$,where $I_C, I_B$,and $I_E$ are the collector,base,and emitter currents,respectively,then:

If $\alpha, \beta$ and $\gamma$ are the lengths of the altitudes of a $\triangle ABC$ with area $\Delta$,then $\frac{\Delta^2}{R^2}\left(\frac{1}{\alpha^2}+\frac{1}{\beta^2}+\frac{1}{\gamma^2}\right)$ is equal to