Which of the following elements does not exhibit variable valency?

$A$ metal $M$ has the electronic configuration $M: 1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^1$. To which block does this metal belong?

Which of the following ions has the highest magnetic moment?

Elements up to atomic number $103$ have been synthesized and studied. If a newly discovered element is found to have an atomic number $106,$ its electronic configuration will be

$Mn^{2+}$ compounds are more stable than $Fe^{2+}$ compounds towards oxidation to their $+3$ state,because

The atomic radius of $Ag$ is closest to