Number of electrons present in the following species Atomic number = number of electrons in neutral species. (i) Be2+⇒ Atomic number =4 It donate 2 electrons and acquire +2 charge. ∴ Number of electrons =2 (ii) H+⇒ Atomic number =1 It donate 1 electron and acquire +1 charge. Number of electrons =0 iii) Na+⇒ Atomic number =11 +1 charge represent donation of 1 electron. Number of electrons =10 iv) Mg+⇒ Atomic number =12 Mg+represent donation of 1 electron. Number of electrons =11 ∴Be2+=2,H+=0 Na+=10,Mg+=11