Chemistry Test 171

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Chemistry Test 171

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Weekly Quiz Competition

Question 1
4 / -1

How many number of molecules and atoms respectively are present in 2.8 litres of a diatomic gas at STP?

A
6.023 x 10²³, 7.5 x 10²³

B
6.023 x 10²³, 15 x 10²²

C
7.5 x 10²², 15 x 10²²

D
15 x 10²², 7.5 x 10²³

Solution
Question 2
4 / -1

Total number of atoms present in 34g of NH₃ is

A
4 x 10²³

B
48 x 10²¹

C
2 x 10²³

D
48 x 10²³

Solution

No. of moles of 34 g of NH₃ = 34/17 = 2

No. of molecules = 2 x 6.023 x 10²³

No. of atoms in one molecule of NH₃ = 4

No. of atoms in 2 molecules of NH₃

= 4 x 2 x 6.023 x 10²³ = 48.18 x 10²³
Question 3
4 / -1

The orientation of an atomic orbital is governed by [2006]

A
Spin quantum number

B
Magnetic quantum number

C
Principal quantum number

D
Azimuthal quantum number

Solution

Magnetic quantum no. represents the orientation of atomic orbitals in an atom. For example p_x, p_y & p_zhave orientation along X-axis, Y-axis & Z-axis
Question 4
4 / -1

If uncertainty in position and momentum are equal, then uncertainty in velocity is : [2008]

A

B

C

D

Solution
Question 5
4 / -1

The measurement of the electron position if associated with an uncertainty in momentum, which is equal to 1 × 10^–18 g cm s^{– 1} . The uncertainty in electron velocity is? (mass of an electron is 9 × 10^{– 28} g)
[2008]

A
1 × 10⁹ cm s^–1

B
1 × 10⁶ cm s^–1

C
1 × 10⁵ cm s^–1

D
1 × 10¹¹ cm s^–1

Solution

Δp = mΔv Substituting the given values of Δx and m, we get 1×10^–18 gcms^–1 = 9×10^–28g × Δv
Question 6
4 / -1

Which among the following elements has maximum atomic radius ?

A
Sodium

B
Potassium

C
Carbon

D
Nitrogen
Solution
The correct answer is Potassium.

Key Points
- Potassium belongs to a group - (1) and period - (IV) of the periodic table. Hence among the given options, Potassium has a maximum atomic radius.
- Carbon and Nitrogen belong to the period - (II) of the periodic table and on the right side hence it is obvious that atomic radii of Carbon and Nitrogen are very much small than Sodium and Potassium.
- Sodium and Potassium belong to a group - (1) and Potassium is placed below Sodium hence the atomic radius of Potassium more than Sodium.
Question 7
4 / -1

The relative atomic masses of all elements have been found with respect to an atom of ________.

A
N-14

B
O-16

C
C-12

D
C-16

Solution

The correct answer is C-12.

The International Union of Chemists selected the most stable carbon isotope (C-12) or ¹²C as the standard for comparison of the atomic masses of various elements.

The mass of C-12 is taken as a 12 atomic mass unit (standard).

A Carbon-12 contains six protons, six neutrons, and six electrons.
Question 8
4 / -1

Until what element was the Law of Octaves determined to be applicable?

A
Cobalt

B
Calcium

C
Potassium

D
Aluminium

Solution

The Law of Octaves was only valid up to the element calcium, because beyond calcium, every eighth element did not have properties that are identical to those of the first element.
Question 9
4 / -1

The qualities of eka-aluminium predicted by Mendeleev are the same as the properties of the element aluminium, which was discovered later.

A
scandium

B
germanium

C
Gallium

D
Aluminium

Solution

Eka-aluminium and gallium are the same elements because the properties of Eka-Aluminium are almost identical to the qualities of the gallium element. Eka-Aluminium is a chemical element that has nearly identical properties to the gallium element. The properties of the elements, such as their atomic mass, density, melting temperature, the formula of chloride, and the formula of oxide, are nearly identical to those anticipated by Mendeleev in his theory.
Question 10
4 / -1

The arrangement of elements in the Modern Periodic Table is based on their\s

A
rising atomic mass in the period\s

B
increasing atomic number in the horizontal rows

C
increasing atomic number in the vertical columns

D
increasing atomic mass in the group

Solution

The elements are listed in ascending order of atomic numbers, with heavier elements at the top of the list. The horizontal rows of the periodic table are referred to as Periods, and the vertical columns of the periodic table are referred to as Groups. The elements in the Modern Periodic Table are divided into seven Periods and eighteen Groups, as shown in the diagram below. The chemical elements are arranged from left to right and top to bottom in order of increasing atomic number, or the number of protons in an atom’s nucleus, which generally corresponds to increasing atomic mass. The elements are arranged from left to right and top to bottom in order of increasing atomic mass.