What is common to all elements ?

Question

In which test tube both water and air are present ? 

Electronic configurations of some elements are : 

(i) 1s² 2s² 2p⁶ 3s² 3p³ 

(ii) 1s² 2s² 2p⁶ 3s² 3p⁶

(iii) 1s² 2s² 2p⁶ 3s² 3p⁴ 

What is common to all elements ? 

(A) Group (B) Period (C) Atomic size (D) B and C

Answer 1

Period is common to all element.