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Standard IX
Chemistry
Question

Which of the following is not a postulate of Dalton's atomic theory?
  1. Atoms are not created or destroyed in chemical change.
  2. Different elements have atoms of different masses.
  3. Atoms combine in simple whole number ratios to form compounds.
  4. Atoms of a single element can have different masses.

A
Atoms of a single element can have different masses.
B
Atoms combine in simple whole number ratios to form compounds.
C
Atoms are not created or destroyed in chemical change.
D
Different elements have atoms of different masses.
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Solution
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Postulates of Dalton's atomic theory:
  1. All matter consists of indivisible particles called atoms.
  2. Atoms of the same elements are similar in shape and mass but differ from the atoms of other elements.
  3. Atoms cannot be created or destroyed.
  4. Atoms of different elements may combine with each other in fixed, simple, whole-number ratios to form elements and compounds.
  5. The atom is the smallest unit of matter that can take part in a chemical reaction.

'Atoms of a single element can have different masses' is not present in postulates of Dalton's atomic theory. It is in fact a limitation of Dalton's atomic theory. Hence, option D is the correct choice.

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Similar Questions
Q1

Which of the following are true according to Dalton’s Atomic Theory?

(i) Atoms can neither be created nor destroyed in a chemical reaction.

(ii) Atoms of different elements have different masses and chemical properties.

(iii) Atoms can be broken down into smaller parts like Protons,Electons And Neutons .

(iv) Atoms of an element have variable chemical properties depending on the Chemical reactions

(v) The relative number and kinds of atoms vary in a given compound.

(vi) Atoms combine in the ratio of small whole numbers to form Compounds.


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Q2
One of the statements of Dalton's atomic theory is given below "compounds are formed when atoms of different elements combine in a fixed ratio. " Which law of chemical combination is not related to this statement?
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Q3
Atoms of the same two elements can combine in different ratios to form different compounds. This law is called the :
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Q4
Isotopes are the atoms of the same element; they have the same atomic number but different mass numbers. Isotopes have a different number of neutrons in their nucleus. If an element exists in two isotopes having atomic masses 'a' and 'b' in the ratio m: n, then average atomic mass will m×a+n×bm+n.
Different isotopes of the same element have the same position in the periodic table. The elements which have single isotope are called monoisotopic elements. Greater is the percentage composition of an isotope, more will be its abundance in nature.

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Q5
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