Atoms and Molecules Test

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Atoms and Molecules Test - 19

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Weekly Quiz Competition

Question 1
1 / -0

The % of Copper and Oxygen in samples of CuO obtained by different methods were found to be the same.
This proves the law of:

A
constant proportions

B
reciprocal proportions

C
multiple proportions

D
conservation of mass.

Solution

According to the law of constant proportions, a chemical compound always contains the same elements combined together in the same proportion by mass.

In CuO, copper and oxygen always combine in the same proportion, irrespective of the source or method of preparation.

So, the correct option is A.
Question 2
1 / -0

Which one of the following properties of an element is not variable?

A
Valency

B
Atomic weight

C
Equivalent weight

D
All of these

Solution

Atomic weight is specific for a particular element and does not change under any circumstances.
Question 3
1 / -0

The value of the Avogadro constant is :

A
$$6.022\times 10^{24}$$

B
$$6.022\times 10^{22}$$

C
$$60.22\times 10^{24}$$

D
$$6.022\times 10^{23}$$
Solution
Correct option : $$D$$

Explanation:
- Avogadro constant is defined as the number of constituent particles per mole of a given substance.
- The value for Avogadro's constant is $$6.022 X 10^{23}$$.
- It is used as the number of units in a mole of any substance.
- For Example: 1 mole of $$CO_2$$ has $$44 \ g$$ and it has $$6.022 \times 10^{23}$$ molecules in it.
Question 4
1 / -0

Number of atoms in $$12$$ gm of $$^{12}_6C$$ is:

A
$$6$$

B
$$12$$

C
$$6.02\times 10^{23}$$

D
$$6\times 6.02\times 10^{23}$$

Solution

The Avogadro number, which is $$6.022 \times 10^{23}$$ is defined as the number of atoms in exactly 12 g of $$^{12}_6C$$ (carbon-12). So, we can say that the number of atoms in 12 gm of carbon-12 is $$6.022 \times 10^{23}$$.
Question 5
1 / -0

_________ is the smallest unit of matter which may or may not have an independent existence, but always takes part in a chemical reaction.

A
An Atom

B
A compound

C
A crystal

D
All the above

Solution

An atom is the smallest unit of matter which takes part in a chemical reaction, it may or may not have an independent existence.

A compound is formed by definite composition of atoms. Example- Water ($$H_2O$$)- there are 2 Hydrogen atoms and 1 oxygen atom.

A crystal is a periodic arrangement of atoms or ions. Example- Cu, NaCl
Question 6
1 / -0

The molecular mass of $$(NH_2)_2CO$$ is :
(Given atomic mass of H = 1, O = 16, C = 12, N = 14.)

A
$$90gm/mole$$

B
$$80gm/mole$$

C
$$60gm/mole$$

D
$$62gm/mole$$

Solution

Molar mass
$$(NH_2)_2CO = 2 \times (14+2)+12+16 = 60 gm/mole$$
Question 7
1 / -0

An atom is different from its ion in:

A
nuclear charge

B
mass number

C
number of electrons

D
number of neutrons

Solution

An ion is formed by gain or loss of electrons from a neutral atom. The number of electrons gained or losses is the charge of that ion. Therefore an atom and an ion differ in the number of electrons.

Hence, the correct option is $$C$$.
Question 8
1 / -0

When two atoms combine to form molecule, then :

A
energy is released

B
energy is absorbed

C
energy is neither released nor absorbed

D
energy may either be released or absorbed

Solution

When two free atoms combine to form a bond, some heat is always evolved which is known as the bond formation energy or the bond energy. Hence, option A is the correct answer.
Question 9
1 / -0

Which of the following is a diatomic element?

A
Bromine

B
Iodine

C
Nitrogen

D
All of the above

Solution

Diatomic elements are all gases, and they form molecules because they don't have full valence shells on their own. The diatomic elements are: Bromine, Iodine, Nitrogen, Chlorine, Hydrogen, Oxygen, and Fluorine.
Question 10
1 / -0

The molecular mass of $$Mg_3N_2$$ is ::
Given atomic mass of $$(N = 14, Mg = 24.)$$

A
$$84gm/mole$$

B
$$98gm/mole$$

C
$$114gm/mole$$

D
$$100gm/mole$$

Solution

Molar mass
$$Mg_3N_2 = 3\times24+2\times14 = 100 gm/mole$$

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Re-Attempt Weekly Quiz Competition

Atoms and Molecules Test - 19

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Atoms and Molecules Test - 19

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SHARING IS CARING

Question 1

constant proportions

reciprocal proportions

multiple proportions

conservation of mass.

Solution

Question 2

Valency

Atomic weight

Equivalent weight

All of these

Solution

Question 3

$$6.022\times 10^{24}$$

$$6.022\times 10^{22}$$

$$60.22\times 10^{24}$$

$$6.022\times 10^{23}$$

Solution

Question 4

$$6$$

$$12$$

$$6.02\times 10^{23}$$

$$6\times 6.02\times 10^{23}$$

Solution

Question 5

An Atom

A compound

A crystal

All the above

Solution

Question 6

$$90gm/mole$$

$$80gm/mole$$

$$60gm/mole$$

$$62gm/mole$$

Solution

Question 7

nuclear charge

mass number

number of electrons

number of neutrons

Solution

Question 8

energy is released

energy is absorbed

energy is neither released nor absorbed

energy may either be released or absorbed

Solution

Question 9

Bromine

Iodine

Nitrogen

All of the above

Solution

Question 10

$$84gm/mole$$

$$98gm/mole$$

$$114gm/mole$$

$$100gm/mole$$

Solution

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