HOTS Questions: Atoms and Molecules - Class 9 MCQ

Democritus and Leucippus suggested that if we go dividing matter, a stage will come when particles obtain can’t be divided further.

Cobalt - Co
Copper - Cu
Sulphur - S
Sodium - Na
Hence, option B.

B is the correct option.In order to have one mole of things, let's say particles, you need to have 6.022⋅1023 particles → this is known as Avogadro's constant and acts as the definition of the mole. So, in one mole of nitrogen gas you have 6.022⋅1023 molecules of nitrogen gas, N2

The diameter of Hydrogen atom is 10⁻¹⁰m. it is the smallest atom among all elemetns.

STM ( scanning tunneling microscope)  is  an instrument for Imaging surfaces at the atomic level. 
John Dalton gave the Atomic theory of Matter. 
Fullerene is an Allotrope of carbon. 
Potassium sulphate is a compound.

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

Atomic mass of Mg is 24. So, 24 g of Mg contains 6.022 x 10²³ atoms. No. of atoms in 0.024 g of Mg =  = 6.022 x 10²⁰ atoms. 

Dalton was the first scientists who use the symbols for elements. The modern symbols are different from symbol proposed by Dalton.

The correct answer is B as  all the statements of option c and d are true about dalton's theory .

Chemical formula of Quick lime is CaO. So, elements present in Quick lime is Calcium and Oxygen.

Mole is also known as chemist dozen. The mass of one twelfth of the mass of one atom of carbon taken as 1u. So, both the statements are correct.

Latin name of Potassium element is Natrium from which symbol of Sodium is derived as Na.

Law of conservation of mass states that, during chemical reaction, the sum of the masses of the reactants and products remains unchanged.

Chemical formula of Calcium phosphide is Ca₃P₂. Valency of Calcium is 2 and Phosphate is 3.

The number of molecules present in one gram molecular mass of a substance is 6.022 × 10²³ molecules called as Avogadro number.

There are 5 atoms in the given ion, in which 1 atom is of Potassium and 4 atoms of Oxygen.

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

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

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

The Dalton’s postulates that Atoms can neither be created nor destroyed are the basis of law of conservation of masses.

Molecular mass of Sodium is 23 u. So, 23 g of sodium is equal to 1 mole. The number of mole in 2.3 g = 2.3 / 23 = 0.1 mole.

A is the correct option.
Nitrate is a polyatomic ion with the chemical formula NO3- Salts containing this anion are called nitrates.
The chemical formula of Phosphide is P-3.
The nitrite ion, which has the chemical formula NO⁻ ₂. Nitrite is widely used throughout chemical and pharmaceutical industries. 
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. PO₄³⁻
 

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