Arrange the oxides $CrO$,$CrO_3$,and $Cr_2O_3$ in the decreasing order of acidic strength.

$Fe$,$Co$ and $Ni$ have valuable catalytic properties in processes involving

Among $K, Ca, Fe,$ and $Zn$,the element which can form more than one binary compound with chlorine is

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:

Which of the following pairs of compounds do not exist?

Explain the trends in $M^{2+}/M$ standard electrode potentials.