Which group of elements is known as halogens? MCQ with Answer and Explanation

Explanation:
Calcium (Ca, Z=20) has configuration 2,8,8,2. 4 shells → Period 4; 2 valence electrons → Group 2. Mg is Group 2, Period 3. Sr is Group 2, Period 5. Be is Group 2, Period 2.

Explanation:
Distilled water is considered the purest form of water because it is obtained by boiling water and condensing the steam, leaving almost all impurities, minerals, and salts behind. Rainwater is relatively pure but dissolves atmospheric gases and dust as it falls.

Explanation:
Bakelite is a thermosetting plastic, heat resistant and electrical insulator. Polythene and PVC are thermoplastics; they soften on heating. Teflon is non-stick.