Q. 165.0( 3 Votes )

An element ‘X’ (Atomic number = 20) burns in the presence of oxygen to form a basic oxide.

a. Identify the element and write its electronic configuration.

b. State its group number and period number in the Modern Periodic Table.

C. Write a balanced chemical equation for the reaction when this oxide is dissolved in water.

Answer :

(a) Since element X burns in the presence of oxygen to form a basic oxide this means that it is metal and it’s atomic number is 20 so it is calcium (Ca). It’s electronic configuration is


Ca20 = 2, 8, 8, 2


(b) We know that group number is equal to valence shell electrons and period is equal to number of shells contain by the element. Element X has 2 valence shell electrons and 4 shells so its group number is 2 and period is 4th.


(c) CaO + H2O Ca(OH)2


Note- Balancing of chemical equation-


(i) Here one Ca atom is in left side and one Ca atom is in right side. So Ca atoms are equal.


(ii) And we shall check that other atoms are equal or not. If the other atoms are equal to both side then the equation is balanced. If the other atoms are not equal then we shall equal them.


Now Ca atoms are equal, H atoms are equal and O atoms are also equal on both sides. So the chemical equation is balanced.


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