'Amoebiasis' (amoebic dysentery) is caused by

At a certain place,the angle of dip is $60^{\circ}$ and the horizontal component of the earth's magnetic field $(B_H)$ is $0.8 \times 10^{-4} ~T$. The earth's overall magnetic field is

If $y = \tan^{-1}(\sec x - \tan x)$,then $\frac{dy}{dx} = $

$A$ large horizontal surface moves up and down in $SHM$ with an amplitude of $1 \, cm$. If a mass of $10 \, kg$ (which is placed on the surface) is to remain continually in contact with it,the maximum frequency of $SHM$ will be ... $Hz$.

The hydroxides and carbonates of sodium and potassium are easily soluble in water,while the corresponding salts of magnesium and calcium are sparingly soluble in water. Explain.

Give the correct order of electrical conductivity of aqueous solution of the following complexes:
$A. [Pt(NH_3)_6]Cl_4$
$B. [Cr(NH_3)_6]Cl_3$
$C. [Co(NH_3)_4Cl_2]Cl$
$D. K_2[PtCl_6]$