Iron becomes passive by ..................... due to formation of .....................
dil. $HCl, Fe_2O_3$
$80\%$ conc. $HNO_3, Fe_3O_4$
conc. $H_2SO_4, Fe_3O_4$
conc. $HCl, Fe_3O_4$
Which of the following ion is diamagnetic
Which of the following is arranged in order of increasing melting point?
When $KMnO_4$ solution is added to hot oxalic acid solution, the decolourisation is slow in the beginning but becomes instantaneous after some time. This is because
Mention the type of compounds formed when small atoms like $H$, $C$ and $N$ get trapped inside the crystal lattice of transition metals. Also give physical and chemical characteristics of these compounds.
An oxide of copper which is red in colour has the formula