Transition elements exhibit variable valencies because they release electrons from the following orbits:

The pair that has similar atomic radii is

State whether the following statements are true or false:
$(i)$ Atomic size increases with an increase in the atomic number of elements.
$(ii)$ The electron gain enthalpy for noble gases is approximately zero.
$(iii)$ The first element of the actinoid series is $Th$ and the last element is $Lu$.
$(iv)$ The general electronic configuration of $d$-orbitals is always $(n-1)d^{1-10}ns^2$.

Which metal wire is used as a conductor of electricity?

$E^o$ for the conversion of $Ce^{+4}$ into $Ce^{+3}$ is $1.74 \ V$. It suggests that

Among the following components of cement,which is present in the highest amount?