AIEEE 2004 (Chemistry) Mock Test

Which one of the following ores is best concentrated by the froth – floatation method?

Beryllium and aluminium exhibit many properties which are similar. But the two elements differ in:

Aluminium chloride exists as a dimer, ${\text{Al}}_2{\text{Cl}}_6$, in solid state as well as in solutions of non-polar solvents such as benzene. When dissolved in water, it gives:

The soldiers of Napoleon's army while at Alps during freezing winter suffered a serious problem as regards to the tin buttons of their uniforms. White metallic tin buttons got converted to grey powder. This transformation is related to:

The $E_{{\text{M}}^{3+}/{\text{M}}^{2+}}^{\circ }$ values for $\text{Cr, Mn, Fe}$ and $\text{Co}$ are $-0.41,+1.57,+0.77$ and $+1.97\text{V}$ respectively. For which one of these metals is the change in oxidation state from $+2$ to $+3$ easiest?