The number of electrons present in the valency shell of a halogen is:

Which of the following remains unchanged on descending a group in the periodic table?

The electron affinity of the elements in group 1 to 7

An alkaline earth metal 

An element in period-3 whose electron affinity is zero.

The element with atomic number 26 will be found in group

The valence shell of element A contains 3 electrons while the valence shell of element B contains 6 electrons. If A combines with B, the probable chemical formula of the compound 

Element 'A' has electronic configuration 2, 7; 'B' has electronic configuration 2, 8, 5 and 'C' has electronic configuration 2, 8, 7. Which two elements will exhibit similar chemical properties?

The total number of electrons present in the first twenty elements of the periodic table is 

The longest period of periodic table is