The species that is isotonic with $_1^3T$ is .....

Which of the following species contain only $1$ electron?

Match the following species with the correct number of electrons present in them:

Species	Number of Electrons
$(i) Be^{2+}$	$(a) 0$
$(ii) H^{+}$	$(b) 10$
$(iii) Na^{+}$	$(c) 2$
$(iv) Mg^{+}$	$(d) 11$

The atomic number of an element is always equal to

$Na^{+}$ ion is isoelectronic with

An element has an atomic weight of $40$ and its electronic configuration is $1s^2 2s^2 2p^6 3s^2 3p^6$. What are its atomic number and the number of neutrons?