Test: Atoms And Molecules - 1

# Test: Atoms And Molecules - 1

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## 10 Questions MCQ Test Science & Technology for UPSC CSE | Test: Atoms And Molecules - 1

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Test: Atoms And Molecules - 1 - Question 1

### 4.48 L of CH4 at STP is equal to______.

Detailed Solution for Test: Atoms And Molecules - 1 - Question 1

Methane (CH4) is a gas and we know for gases at STP,
22.4 L = 1 mole gas
⇒ 4.48 L of methane gas = 4.48/22.4 = 0.2 moles
∵ 1 mole of CH4 = 6.022 x 1023 molecules of methane
∴ 0.2 mole of CH4 = 6.022 x 1023 x 0.2 = 1.2 x 1023 molecules

Test: Atoms And Molecules - 1 - Question 2

### The same proportion of carbon and oxygen in CO2 obtained from different sources proves the law of_______.

Detailed Solution for Test: Atoms And Molecules - 1 - Question 2

The law of definite proportion states that a compound always contains exactly the same proportion of elements by mass. Thus, no matter where the carbon dioxide comes from, it always carbon and oxygen in the ratio by mass.

Test: Atoms And Molecules - 1 - Question 3

### If isotopic distribution of C-12 and C-14 are 98% and 2% respectively, then number of C-14 atoms in 12 g of carbon is________.

Detailed Solution for Test: Atoms And Molecules - 1 - Question 3

In 12 g of carbon, the amount of C-14
= 12 × 2/100 = 0⋅24g
∴ C-14 atoms in 0.24g = (0⋅24×6⋅02×1023)/14
= 1⋅03×1022 atoms.

Test: Atoms And Molecules - 1 - Question 4

1.0 mole CO2 contains

Detailed Solution for Test: Atoms And Molecules - 1 - Question 4
• 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.

Test: Atoms And Molecules - 1 - Question 5

Identify the correct symbol of Gold.

Detailed Solution for Test: Atoms And Molecules - 1 - Question 5

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

Test: Atoms And Molecules - 1 - Question 6

The percentage of hydrogen in water is______.

Detailed Solution for Test: Atoms And Molecules - 1 - Question 6

There is also one mole of oxygen atoms weighing 16.00 grams in the mole of water and that of hydrogen is 2.00 gram.
To get the percentage of hydrogen, divide the 2 by 18 and multiply by 100.
i.e. Percentage of hydrogen = (2/18) x 100 = 11.11%

Test: Atoms And Molecules - 1 - Question 7

The combining capacity of an element is called

Detailed Solution for Test: Atoms And Molecules - 1 - Question 7
• 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.
Test: Atoms And Molecules - 1 - Question 8

One atomic mass unit of carbon-12 is

Detailed Solution for Test: Atoms And Molecules - 1 - Question 8

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.

Test: Atoms And Molecules - 1 - Question 9

Which is not represented by 1 mole of nitrogen gas?

Detailed Solution for Test: Atoms And Molecules - 1 - Question 9

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.

Test: Atoms And Molecules - 1 - Question 10

Numerical value of Avogadro’s number is

Detailed Solution for Test: Atoms And Molecules - 1 - Question 10

Avogadro's number, number of unit in one mole of any substance equal to 6.023 * 1023 . The units may be electrons, atoms, ions or molecules, depending on the nature of the substance and the character of the reaction.

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