Test: Atoms And Molecules - 1 - Class 9 MCQ

The correct answer is (b) 1 g of hydrogen and 8 g of oxygen. This is because water (H2O) consists of two hydrogen atoms and one oxygen atom. By mass, hydrogen contributes approximately 11.1% and oxygen contributes approximately 88.9% to the mass of water. Thus, from 9g of water, we get approximately 1 g of hydrogen and 8 g of oxygen.

The correct answer is (b) Co. The symbol for the element cobalt is "Co" according to the periodic table.

The correct answer is (a) 3g of carbon and 4g of oxygen. In carbon monoxide (CO), one carbon atom combines with one oxygen atom. The molar mass of CO is 12g/mol + 16g/mol = 28g/mol. Since the total mass is 7g, it means we have approximately 0.25 moles of CO. For each mole of CO decomposed, we obtain 1 mole of carbon and 1 mole of oxygen. Hence, from 0.25 moles of CO, we get approximately 0.25 moles of carbon and 0.25 moles of oxygen, which translates to 3g of carbon and 4g of oxygen.

• One mole of CO₂ = one mole of C = 6.02×10²³ atoms of carbon.
• One mole of CO₂ = two moles of O = 2×6.02×10²³= 12.04×10²³ atoms of oxygen.
• One mole of CO₂​ = 6.02×10²³ molecules of CO₂

​Note: 6.02×10²³ is Avogadro's number and represents number of atoms/molecules present in one mole of substance.

The chemical symbol for gold is Au, taken from the Latin word for gold- Aurum. Its atomic number is 79.

The correct answer is (d) 35.5. The atomic mass unit (amu) of chlorine is approximately 35.5 g/mol. This is the average atomic mass of chlorine isotopes based on their natural abundance.

• The combining capacity of an element is known as its valency.
• Valency is the number of valence electrons in outer shell that take part in the chemical reaction.

One atomic mass unit is defined as one-twelfth of the one-carbon of one carbon - 12 atom because C - 12 is chosen as the standard form.

1 gram - atom nitrogen corresponds to mass of one mole of the nitrogen atom is grams that is one gram - atom of nitrogen represents 28 gms of nitrogen. 
It is equal to 6.023 * 10²³ N atoms, but not  
6.023 * 10²³ N2 molecules.
 

• Option A: This symbol is not the correct symbol proposed by Dalton for Hydrogen.


• Option B: This symbol is not the correct symbol proposed by Dalton for Hydrogen.


• Option C: This symbol is the correct symbol proposed by Dalton for Hydrogen. It consists of a circle with a dot in the center.


• Option D: This symbol is not the correct symbol proposed by Dalton for Hydrogen.

Therefore, the correct symbol for Hydrogen as proposed by Dalton is option C, which is a circle with a dot in the center. This symbol has been widely accepted and used to represent Hydrogen in chemical equations and formulas.