An atom has mass number 31 and 16 neutrons. Its atomic number is: MCQ with Answer and Explanation

Explanation:
Niels Bohr proposed his model in 1913 to overcome the defects of Rutherford's model. He stated that electrons revolve around the nucleus in specific, discrete circular orbits (shells) with fixed energy, and they do not radiate energy while in these orbits, explaining atomic stability.

Explanation:
Finely divided nickel is used as catalyst for hydrogenation of unsaturated oils to saturated fats. Platinum and palladium can also be used but are more expensive. The reaction occurs at about 150°C with H₂ gas. Nickel catalyst is prepared by reducing NiO with H₂. This is an important industrial process for making margarine and shortenings.

Explanation:
Valence electrons are the electrons in the outermost shell. Configuration 2,8,2 means K=2, L=8, M=2. The outermost shell M has 2 electrons, so valency is 2, typical of Group 2 metals (Mg). These atoms lose 2 electrons to form M²⁺. The number of valence electrons determines the group in the periodic table. Elements with 2 valence electrons belong to Group 2 (alkaline earth metals).