Some Basic Concepts of Chemistry JEE JEE Main| JEE Main Important Questions

Q 1 :
0.05 cm thick coating of silver is deposited on a plate of 0.05 $m^{2}$ area. The number of silver atoms deposited on plate are _________ $\times 10^{23}$ . (At mass Ag = 108, d = 7.9 g $c m^{- 3}$ ) [2024]

0%

(11) Volume of silver = thickness $\times$ area of plate

= 0.05 cm $\times$ 0.05 $m^{2}$

= 0.05 cm $\times$ 0.05 $\times$ ${(100 c m)}^{2}$

= 25 $c m^{3}$

Mass of silver deposited = density $\times$ volume

= 7.9 $g c m^{- 3} \times$ 25 $c m^{3}$

= 197.5 g

Moles of silver deposited(n) = $\frac{M a s s o f s i l v e r d e p o s i t e d}{m o l a r m a s s o f s i l v e r}$

= $\frac{197.5 g}{108 g m o l^{- 1}}$

= 1.8287 mol

Atoms of silver deposited = $n \times N_{A}$ atoms

= 1.8287 $\times$ 6.022 $\times 10^{23}$

= 11.01 $\times 10^{23}$ atoms

Q 2 :
$2.8 \times 10^{- 3}$ mol of ${CO}_{2}$ is left after removing $10^{21}$ molecules from its $‘ x ’$ mg sample. The mass of ${CO}_{2}$ taken initially is

Given: $N_{A} = 6.02 \times 10^{23} {mol}^{- 1}$ [2025]

48.2 mg
98.3 mg
150.4 mg
196.2 mg

1

2

3

4

(4)

$10^{21} molecules = \frac{10^{21}}{6.02 \times 10^{23}} mol = 1.66 \times 10^{- 3} mol$

Initial moles = mole left + mole removed

Initial moles $= 2.8 \times 10^{- 3} mol + 1.66 \times 10^{- 3} mol$

$= 4.46 \times 10^{- 3} mol$

$Initial mass = Initial moles \times molar mass$

$= 4.46 \times 10^{- 3} mol \times 44 {g mol}^{- 1}$

$= 196.24 \times 10^{- 3} g = 196.24 mg$

Q 3 :
Among $10^{- 9}$ g (each) of the following elements, which one will have the highest number of atoms?

Element: Pb, Po, Pr and Pt [2025]

Po
Pr
Pb
Pt

1

2

3

4

(2)

$Number of atoms = \frac{Given mass}{Atomic mass}$

As given mass is same for the four elements,

$number of atoms \propto \frac{1}{Atomic mass} .$

Po and Pb are present in 6th period, p block. Pt is present in 5d series. Pr is present in 4f series. As Pr is placed before Po, Pb and Pt in periodic table, it has least atomic mass. As it has least atomic mass, it has most number of atoms.

Topic Question Set

Q 1 :
0.05 cm thick coating of silver is deposited on a plate of 0.05 $m^{2}$ area. The number of silver atoms deposited on plate are _________ $\times 10^{23}$ . (At mass Ag = 108, d = 7.9 g $c m^{- 3}$ ) [2024]

0%

Q 2 :
$2.8 \times 10^{- 3}$ mol of ${CO}_{2}$ is left after removing $10^{21}$ molecules from its $‘ x ’$ mg sample. The mass of ${CO}_{2}$ taken initially is

Given: $N_{A} = 6.02 \times 10^{23} {mol}^{- 1}$ [2025]

Q 3 :
Among $10^{- 9}$ g (each) of the following elements, which one will have the highest number of atoms?

Element: Pb, Po, Pr and Pt [2025]

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Topic Question Set

Q 1 : 0.05 cm thick coating of silver is deposited on a plate of 0.05 m2 area. The number of silver atoms deposited on plate are _________ ×1023. (At mass Ag = 108, d = 7.9 g cm-3) [2024]

0%

Q 2 : 2.8×10-3 mol of CO2 is left after removing 1021molecules from its ‘x’ mg sample. The mass of CO2 taken initially is Given: NA=6.02×1023 mol-1 [2025]

Q 3 : Among 10-9 g (each) of the following elements, which one will have the highest number of atoms? Element: Pb, Po, Pr and Pt [2025]

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Q 1 :
0.05 cm thick coating of silver is deposited on a plate of 0.05 $m^{2}$ area. The number of silver atoms deposited on plate are _________ $\times 10^{23}$ . (At mass Ag = 108, d = 7.9 g $c m^{- 3}$ ) [2024]

Q 2 :
$2.8 \times 10^{- 3}$ mol of ${CO}_{2}$ is left after removing $10^{21}$ molecules from its $‘ x ’$ mg sample. The mass of ${CO}_{2}$ taken initially is

Given: $N_{A} = 6.02 \times 10^{23} {mol}^{- 1}$ [2025]

Q 3 :
Among $10^{- 9}$ g (each) of the following elements, which one will have the highest number of atoms?

Element: Pb, Po, Pr and Pt [2025]