MDCAT ECAT Chemistry MCQs with Answers – All Units – Page 37

Question 721 Atomic Structure

How many unpaired electrons are present in a ground-state iron atom (Z = 26)?

Correct answer D. 4

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Question 722 Atomic Structure

What is the ground-state electronic configuration of chromium (Z = 24)?

Correct answer D. [Ar] 3d⁵ 4s¹

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Question 723 Atomic Structure

What is the electronic configuration of the Fe³⁺ ion (Z of Fe = 26)?

Correct answer C. [Ar] 3d⁵

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Question 724 Atomic Structure

Why are positive rays deflected less than cathode rays by the same electric or magnetic field?

Correct answer A. Positive ions are much heavier than electrons

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Question 725 Atomic Structure

What is the energy of a photon of wavelength 600 nm (h = 6.626 × 10⁻³⁴ J s, c = 3.0 × 10⁸ m s⁻¹)?

Correct answer D. 3.31 × 10⁻¹⁹ J

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Question 726 Atomic Structure

What is the energy of one photon of frequency 1.0 × 10¹⁵ Hz (h = 6.63 × 10⁻³⁴ J s)?

Correct answer D. 6.63 × 10⁻¹⁹ J

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Question 727 Atomic Structure

According to Planck’s quantum theory, the energy of a photon is ____

Correct answer D. inversely proportional to its wavelength

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Question 728 Atomic Structure

According to Planck’s quantum theory, energy is emitted or absorbed ____

Correct answer A. discontinuously in small packets called quanta

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Question 729 Atomic Structure

How many orbitals are present in the third shell (n = 3)?

Correct answer A. 9

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Question 730 Atomic Structure

What is the maximum number of electrons that the fourth shell (n = 4) can hold?

Correct answer C. 32

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Question 731 Atomic Structure

Which set of quantum numbers (n, l, m, s) is NOT allowed for an electron?

Correct answer A. n = 2, l = 2, m = 0, s = +½

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Question 732 Atomic Structure

Which quantum number mainly determines the shape of an orbital?

Correct answer B. Azimuthal quantum number (l)

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Question 733 Atomic Structure

Which d orbital has its four lobes lying along the x and y axes?

Correct answer B. d(x²−y²)

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Question 734 Fundamental Concepts of Chemistry

Equal masses of the following gases are taken. Which sample contains the largest number of molecules?

Correct answer C. CH₄

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Question 735 Fundamental Concepts of Chemistry

At STP, 11.2 dm³ of which gas has the greatest mass?

Correct answer C. CO₂

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Question 736 Fundamental Concepts of Chemistry

6.0 g of H₂ reacts with excess N₂ (N₂ + 3H₂ → 2NH₃) and 25.5 g of NH₃ is obtained. What is the percentage yield?

Correct answer B. 75%

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Question 737 Fundamental Concepts of Chemistry

In a balanced chemical equation, the mole ratio between reactants and products is obtained from the ____

Correct answer A. coefficients of the balanced equation

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Question 738 Atomic Structure

In a discharge tube with a perforated cathode, positive (canal) rays travel ____

Correct answer C. towards the cathode and pass through holes in it

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Question 739 Atomic Structure

For which gas in the discharge tube do positive rays have the largest e/m value?

Correct answer A. Hydrogen

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Question 740 Atomic Structure

Who first observed canal (positive) rays in a discharge tube?

Correct answer D. Eugen Goldstein

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