Answers : Fill in the blanks.
Answer 1) During a chemical reaction, the sum of the masses of the reactants and products remain unchanged.
In a reaction masses of the reactants and products always remains the same.
Answer 2) In a pure chemical compound, elements are always present in a definite proportion by mass.
It is observed that in a chemical reaction the elements are found in definite proportion by mass.
Answer 3) Clusters of atoms that act as an ion are called polyatomic ions.
Polyatomic ions are those ions which consits of atoms more than two in their molecule.
Answer 4) In ionic compounds, the charge on each ion is used to determine the chemical formula of the compound.
The charges on the molecule helps to determine the chemical formula of any compound.
Answer 5) The Avogadro constant 6.022 X 
is defined as the number of atoms in exactly 12 g of carbon-12
Avogadro used carbon-12 as the standard reference element fpr determining its molecules.
Answer 6) Mass of 1 mole of a substance is called its molar mass or molecular weight.
A molecular weight of an atom to define its number of moles.
Answer 7) The abbreviation used for length names of elements are termed as their Symbols.
The abbreviation used for the length of names of elements are called as symbols.
Answer 8) A chemical formula is also known as a true formula or molecular formula.
The term chemical formula determines the number of chemical components present in it.
Answer 9) Those ions which are formed from single atoms are called monoatomic ions.
The ions made up from single atoms are called as monoatomic ions.
Answer 10) Ionic compounds are formed by the combination between metal and nonmetal.
The ionic compounds are usually bonded by the ionic bonds in a compound.
Answer 11) The valency of an ion is equal to the charge on the ion.
Valency of any ion is always equal to the charge on that ion.
Answer 12) Mole is a link between the mass of a substance and number of formula units.
Usually the mole forms a link to define the mass of the substance and its formula.
Answer 13) The SI unit of amount of a substance is mole.
Mole is considered to be the SI unit for aount of substance of any chemical compound.
Answer : true or false.
Answer 1) Formula mass of 
O is 62 amu True
As we know there are 2 moles of Na and one mole of O so it will be (2 X 23) + 16 = 62 amu.
Answer 2) Those particles which have more or less electrons than the normal atoms are called ions True
We call ions to those atoms which hav more or less electrons in their normal atoms
Answer 3) Formula for sulphur dioxide is S
. False
The formula for sulphur dioxide is S
as the name di suggests two molecules.
Answer 4) Molar mass of ethyne (C2H2) is 26 g/mol True.
As the ethyene molecule consists of 2 C atoms and 2 H atoms it will be (12 X 2) + (2 X 1) = 26
Answer 5) 22 gm of CO2 consists of 1 mole. False
The 1 mole of C
contains 1 C atom and 2 O atoms (12) + (16 X 2) = 44
Answer 6) Number of molecules in 32 gram of oxygen is 6.02 x 
. False
Only 1 moles of any substance will consist of 6.02 x molecules.
Answer 7) Water is an atom False.
Water is a molecule of 2 atoms namely hydrogen and oxygen.
Answer 8) Formula for sulphur dioxide is S
true.
As the name suggest sulphur along with two oxygen in it.
Answer 9) Clusters of atoms that act as an ion is called polyatomic ion. True
The clusters of ions from different atoms of the elements can be called as polyatomic ions.
Answer 10) Mass of 1 mole of a substance is called its formula mass. False.
As in formula mass we take the sum of the atomic weights of atoms in a molecule. And for 1 mole of a substance it is called as molar mass.
Answer 11) In a pure chemical compound, elements are always present in a definite proportion by mass. True
In any chemical reaction, the pure chemical compound is always found to have elements with definite proportion to their masses.
