Which of the following statements is not correct regarding calcination?

$A$ plane mirror is placed at the bottom of a tank containing a liquid of refractive index $\mu$. $P$ is a small object at a height $h$ above the mirror. An observer $O$,vertically above $P$ outside the liquid,sees $P$ and its image in the mirror. The apparent distance between these two will be

If the best and the worst paper never appear together,then in how many ways can six examination papers be arranged?

An object $2.4 \; m$ in front of a lens forms a sharp image on a film $12 \; cm$ behind the lens. $A$ glass plate $1 \; cm$ thick,of refractive index $1.50$ is interposed between the lens and the film with its plane faces parallel to the film. At what distance (from the lens) should the object be shifted to be in sharp focus on the film (in $; cm$)?

Which of the following is an oxoacid?

After absorbing a slowly moving neutron of mass $m_N$ (momentum $\sim 0$),a nucleus of mass $M$ breaks into two nuclei of masses $m_1$ and $5m_1$ $(6m_1 = M + m_N)$. If the de-Broglie wavelength of the nucleus with mass $m_1$ is $\lambda$,then the de-Broglie wavelength of the other nucleus will be: