Which change occurs when a barium atom loses two electrons? (1) it becomes a negative ion and its radius decreases.(2) it becomes a negative ion and its radius increases.(3) it becomes a positive ion and its radius decreases.(4) it becomes a positive ion and its radius increases.

When a barium atom loses two electrons it becomes a positive ion and its radius decreases. Barium (Ba) has atomic number 56 so it has 2 electrons in first shell of an atom to become stable according to duplet rule. Then other 52 electrons revolve in the shells according to octet rules.

Another 2 electrons are in the outermost shell. To become stable electrons lose to form barium ions (Ba+2). Hence, by losing 2 electrons the outermost shell will be diminished so its radius decreases and by losing electrons it becomes positive ions.

The correct answer is option 3, It becomes a positive ion and its radius decreases

Explanation:

As per the Octet rule, Barium has 2 electrons in its outermost shell. When it loses the two electron it gains two positive charge i.e Ba2+. As the barium loses the two electron from its outermost shell, the outermost shell becomes vacant and thus is no more considered as a part of atomic geometry of the barium atom and since the outermost shell is considered negligible the radius of barium atom reduces automatically.  

the answer is na (sodium)