Exercise

In a qualitative analysis when ${\mathrm{H}}_2\mathrm{S}$ is passed through the solution of a salt acidified with $\mathrm{HCl}$, a black precipitate is obtained. On boiling the precipitate with dil. ${\mathrm{HNO}}_3$, it forms a solution of blue colour. Addition of an excess of an aqueous solution of ammonia to this solution will give ________. 

Electronic configuration of a transition element $\mathrm{X}$ in $+3$ oxidation state is $\left[\mathrm{Ar}\right]3{\mathrm{d}}^5$. What is its atomic number?

What is the colour of potassium dichromate?

Actinoids are _______ due to presence of unpaired $5\mathrm{f}$ electrons.

There are $14$ elements in actinoid series. Which of the following elements does not belong to this series?

Although Zirconium belongs to $4\mathrm{d}$ transition series and Hafnium to $5\mathrm{d}$ transition series even then they show similar physical and chemical properties because _____.

In which of the following outermost orbit will show the maximum number of oxidation states? 

Which of the following factor may be regarded as the main cause of lanthanide contraction?