The highest oxidation state of $Mn$ is shown by

Which of the following are amphoteric oxides?
$Mn_2O_7, CrO_3, Cr_2O_3, CrO, V_2O_5, V_2O_4$

Which of the following metals becomes passive when treated with concentrated $HNO_3$?

Which of the following statements are correct?
$A$. The $M^{3+}/M^{2+}$ reduction potential for iron is greater than manganese.
$B$. The higher oxidation states of first row $d$-block elements get stabilized by oxide ion.
$C$. Aqueous solution of $Cr^{2+}$ can liberate hydrogen from dilute acid.
$D$. Magnetic moment of $V^{2+}$ is observed between $4.4-5.2 \ BM$.
Choose the correct answer from the options given below:

The incorrect statement$(s)$ among $(a)-(c)$ is (are) :-
$(a)$ $W(VI)$ is more stable than $Cr(VI)$
$(b)$ In the presence of $HCl$,permanganate titrations provide satisfactory results.
$(c)$ Some lanthanoid oxides can be used as phosphors.

The correct order of basicity of oxides of vanadium is