NCERT Exemplar Class 11 Chemistry Chapter 9 MCQ

(a) OxygenExplanation:The mass-abundance of the nine most abundant elements in the Earths crust is approximately: oxygen 46%, silicon 28%, aluminium 8.2%, iron 5.6%, calcium 4.2%, sodium 2.5%, magnesium 2.4%, potassium, 2.0%, and titanium 0 .61%.Hydrogen is 0.14% on earths crust and other elements occur at less than 0.15%.

(c) Nascent HydrogenExplanation:A hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral atom contains a single positively charged proton and a single negatively charged electron bound to the nucleus by the Coulomb force. Atomic hydrogen constitutes about 75% of the baryonic mass of the universe.In everyday life on Earth, isolated hydrogen atoms (called “atomic hydrogen”) are extremely rare. Instead, a hydrogen atom tends to combine with other atoms in compounds, or with another hydrogen atom to form ordinary (diatomic) hydrogen gas, H2. “Atomic hydrogen” and “hydrogen atom”

(b) ReducingExplanation:Hydrogen acts as a good reducing agent means, when hydrogen gas is passed over hot metallic oxides of copper, lead, iron, etc. it removes oxygen from them and thus reduces them to their corresponding metal. Let us consider the following example, in each of which metallic oxide react with hydrogen. Metallic oxide act as oxidizing agents and hydrogen acts as a reducing agent.

(b) 50 mlExplanation:$ As 10 ml of oxygen is obtained at STP from H2O2 = 1$ mlTherefore,$500 ml of O2 is obtained at STP = 50$ ml

(a) AbundantExplanation:Hydrogen is considered as the most common and abundant element. The element Hydrogen has only one proton and one electron and is the only element which has no neutrons. Therefore it is considered as the simplest element in the universe and gives a valid reason for it to be the most abundant and common element in the universe. As per estimation from the Jefferson Lab, approximately 90 percent of the visible universe is framed by Hydrogen proving that being in the simplest form, this element is the most common and abundant element in the universe.