Across the lanthanide series, the basicity of the lanthanide hydroxides _____.

$\mathrm{Cu}+\mathrm{X}⟶\mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2+2{\mathrm{H}}_2\mathrm{O}+2{\mathrm{NO}}_2$

Here $\mathrm{X}$ is:

Assertion: The $4\mathrm{f}$ and $5\mathrm{f}$ inner transition series of elements are placed between the $\mathrm{d}-$block elements in the periodic table.

Reason: The $4\mathrm{f}-$ and $5\mathrm{f}-$ inner transition series of elements are placed at the bottom of the periodic table.
($\mathrm{i}$) This prevents the undue expansion of the periodic table i.e., maintains its structure.
($\mathrm{ii}$) This preserve the principle of classification by keeping elements with similar properties in a single column.

For the reaction, ${\mathrm{Cr}}_2{\mathrm{O}}_7^{2-} \stackrel{\mathrm{pH} =\mathrm{x}}{\to } {\mathrm{CrO}}_4^{2-}\stackrel{\mathrm{pH} =\mathrm{y}}{\to }{\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}$$\mathrm{pH}$ values $\text{'}\mathrm{x}\text{'}$ and $\text{'}\mathrm{y}\text{'}$ can be