Atoms And Molecules - MCQ Test (22-11-2017) - Class 9 MCQ

Leucippus and Democritus are widely regarded as the first atomists in the Greek tradition. They had suggested that if we go dividing matter, a stage will come when particles obtain can’t be divided further.

According Dalton’s atomic theory, atoms are the ultimate indivisible particle of matter and atoms of the same element have same atomic masses, size and chemical properties.

Number of moles of Helium = Mass of Helium / Molar mass of Helium = 40 / 4 = 10 moles. Atomic mass or molar mass of Helium is 4 u.

One mole of N₂ is equal to 28 g of nitrogen or 6.022×10²³ molecules.

The diameter of Hydrogen atom is 10⁻¹⁰m. It is the smallest atom among all elements.

Law of conservation of mass states that matter can neither be created not destroyed. Therefore, during a chemical reaction, the sum of the masses of the reactants and products remains unchanged.

The chemical formula of Quick lime is CaO. So, Calcium (Ca) and Oxygen (O) elements are present in Quick lime.

Both the statements are correct. A mole is also known as a chemist's dozen. A mole, just like a dozen, is a common counting unit. A counting unit is a convenient number that makes it easier to count objects. The mass of one-twelfth of the mass of one atom of Carbon is taken as 1 u.

Dalton was the first scientist who used the symbols to represent the elements of modern chemistry. The modern symbols are different from the symbols proposed by Dalton. Dalton, considered as the father of modern atomic theory, made a logbook entry that day titled, "Observations on the Ultimate Particles of Bodies and their Combinations."

An atom cannot exist independently. The law of constant proportions is applicable only to pure chemical compounds.
So, only statement B is correct.

The valency of Calcium is 2 (Ca²⁺)and the valency of the Phosphide ion is 3 (P^3-). A chemical compound is always electrically neutral; so the positive and negative valencies of the ions or radicals present in calcium phosphide should add up to zero. Therefore, the chemical formula of calcium phosphide is Ca₃P₂

Gram molecular mass is the mass in grams of one mole of a molecular substance. One mole contains  6.022×10²³  molecules. This is known as Avogadro number. Therefore, one gram molecular mass of a substance has 6.022×10²³ molecules. 

Latin name of Potassium element is Kalium from which symbol of Potassium is derived as K.

The basis of the Law of conservation of mass is the following postulate given by Dalton:-"Atoms can neither be created nor destroyed in a chemical reaction"

Atomic mass of hydrogen is 1 u. Mass of one mole of Hydrogen is equal to 1 g. Therefore, mass of 0.5 mole of Hydrogen atom will be 0.5×1=0.5g

Number of moles in 60 g of Calcium = Given mass of Calcium / Atomic mass of Calcium = 60/40 = 1.5 mol

There are 5 atoms in the phosphate ion - 1 atom of Phosphorus and 4 atoms of Oxygen.

Sulphate and oxalate ions are anions while magnesium and ammonium ions are cations.

H₂SO₄ is composed of 2 Hydrogen, 1 Sulphur and 4 Oxygen atoms. It relative molecular mass is 98.

Short hand representation of an element is called symbol. Symbol of an element is derived from English name or Latin name.

Atomic mass of magnesium is 24. Atomic mass of sulphur is 32. Therefore, the ratio of magnesium and sulphur by mass in magnesium sulphide (MgS) is 24:32 or 3:4

Molecular mass of Sodium is 23 u. So, 23 g of Sodium (Na) is equal to 1 mole of Na.

Number of moles of Na present in 2.3 g of Na = Given mass of Na / Molar mass of Na = 2.3 / 23 = 0.1 mole

A mole is defined as the amount of a substance which contains the same number of elementary entities (e.g. atoms, molecules, ions, electrons, photons) as atoms in 0.012 kilograms of carbon-12. Gram atomic mass is the mass (in grams) of one mole of atoms in a monatomic element. It is numerically equal to the relative atomic mass (or atomic weight) in grams. Gram molecular mass is the mass (in grams) numerically equal to the molecular weight of a substance or the sum of all the atomic masses in its molecular formula.

Latin name of sodium is Natrium. Therefore, the symbol of Sodium is Na.

Formula unit mass of ZnCl₂ is (66+35.5×2=137u)

Atomic mass of Zn is 66 and the atomic mass of Cl is 35.5

Fixed number of atoms or molecules present in gram atomic mass of an atom or molecules is 6.022 × 10²³.This number is known as Avogadro constant.

Dalton was the first to state that the smallest indivisible portion of matter is an atom. The law of conservation of mass was given by A.Lavoisier. The law of constant proportions was stated by Louis Proust. The molecules of noble gas elements are monoatomic in nature.

The Latin name of Silver is Argentum. The symbol of Silver is Ag.

Gram atomic mass of an element and the gram molecular mass of a compound contain the same number of molecules, which is equal to 6.022×10²³ molecules.

Molecular mass of H₂O₂ is 34 u. So, 34 g of hydrogen peroxide will contain 1 moles. Therefore, 17 g of hydrogen peroxide will contain 17/34 moles or 1/2mole.