Total internal reflection of light is possible when light enters from

Which of the following statements is not correct?

The value of $\left|\begin{array}{lll}1990 & 1991 & 1992 \\ 1991 & 1992 & 1993 \\ 1992 & 1993 & 1994\end{array}\right|$ is

Two point charges $-q$ and $+q$ are located at points $(0, 0, -a)$ and $(0, 0, a)$ respectively. The potential at a point $(0, 0, z)$ where $z > a$ is

The equation of the sphere passing through the points $(1,0,0)$, $(0,1,0)$, and $(1,1,1)$ and having the smallest radius is:

The cubic equation whose roots are the squares of the roots of $x^3-2x^2+10x-8=0$ is