An atom with atomic number $20$ is most likely to combine chemically with the atom whose atomic number is

If an electron is transferred from $B$ to $A$,then the reaction is possible when:

Which one of the following reactions does not occur?

Observe the following data ($ \Delta_i H_1, \Delta_i H_2 $ and $ \Delta_{eg} H $ represent the first,second ionisation enthalpies and electron gain enthalpy respectively).

Element	$ \Delta_i H_1 $ $( kJ \ mol^{-1} )$	$ \Delta_i H_2 $ $( kJ \ mol^{-1} )$	$ \Delta_{eg} H $ $( kJ \ mol^{-1} )$
$ I $	$ 520 $	$ 7300 $	$ -60 $
$ I.I $	$ 490 $	$ 3051 $	$ -48 $
$ III $	$ 1681 $	$ 3374 $	$ -328 $
$ IV $	$ 2372 $	$ 5251 $	$ +48 $

Using the data,identify the most reactive metal.

Which of the following pairs has both members from the same group of the periodic table?

$Mg^{2+}$ is . . . . . . than $Al^{3+}$.