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UPCET / UPSEE Chemistry — practice questions

Explore 81 free Chemistry questions in UPCET / UPSEE Chemistry. Open each question or exercise to read its content, reference answers and available explanation.

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Chemistry questions and exercises with answers

Showing questions 1–30 of 81.

The modern periodic law states that the physical and chemical properties of elements are periodic functions of:Read the answer and worked solution →Elements of the modern periodic table are classified into how many blocks based on the differentiating electron?Read the answer and worked solution →Across a period from left to right, the atomic radius generally:Read the answer and worked solution →Which element has the highest first ionization energy in period 2?Read the answer and worked solution →Which of the following arrangements is in correct order of increasing electronegativity (Pauling scale)?Read the answer and worked solution →The element with electronic configuration $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^3$ belongs to which group and period?Read the answer and worked solution →The wave number $\bar{\nu}$ of electromagnetic radiation is defined asRead the answer and worked solution →In vacuum, the velocity of electromagnetic radiation isRead the answer and worked solution →A photon has wavelength $400\,nm$. Its frequency is approximatelyRead the answer and worked solution →The wave number of a photon of frequency $6 \times 10^{14}\,Hz$ (in vacuum) isRead the answer and worked solution →According to Planck's quantum theory, energy is emitted or absorbed in discrete packets calledRead the answer and worked solution →The energy of a photon of wavelength $\lambda$ is given byRead the answer and worked solution →A photon of wavelength $300\,nm$ has approximately what energy in eV? (Use $hc = 1240\,eV\,nm$.)Read the answer and worked solution →In the photoelectric effect, the kinetic energy of the ejected electron depends onRead the answer and worked solution →The threshold frequency $\nu_0$ for a metal is the minimum frequencyRead the answer and worked solution →Light of frequency $\nu = 2\nu_0$ ejects photoelectrons from a metal with threshold frequency $\nu_0$. The maximum KE of the photoelectrons isRead the answer and worked solution →Rutherford's $\alpha$-particle scattering experiment used a thin foil of which metal?Read the answer and worked solution →For a hydrogen-like atom of nuclear charge $Z$, the radius of the $n$th Bohr orbit scales asRead the answer and worked solution →The energy of the $n$th Bohr orbit of a hydrogen-like atom isRead the answer and worked solution →The ratio of the radii of the third Bohr orbit of $He^+$ and the first Bohr orbit of $H$ isRead the answer and worked solution →The velocity of the electron in the $n$th Bohr orbit of a hydrogen-like atom is proportional toRead the answer and worked solution →The energy required to remove the electron from the first excited state ($n=2$) of $He^+$ isRead the answer and worked solution →Which series of the hydrogen spectrum lies entirely in the *visible* region?Read the answer and worked solution →Rydberg's formula for the wave number of a hydrogen spectral line isRead the answer and worked solution →The longest wavelength line in the Lyman series of hydrogen corresponds to the transitionRead the answer and worked solution →The de Broglie wavelength of a particle of mass $m$ and momentum $p$ isRead the answer and worked solution →The de Broglie wavelength of an electron in the $n$th Bohr orbit, in terms of the orbit radius $r_n$, isRead the answer and worked solution →An electron is accelerated through a potential difference of $100\,V$. Its de Broglie wavelength is approximatelyRead the answer and worked solution →Heisenberg's uncertainty principle relates the uncertainties in position and momentum asRead the answer and worked solution →The minimum uncertainty in the velocity of an electron whose position is known to within $\Delta x = 0.1\,nm$ is approximatelyRead the answer and worked solution →

Worked practice questions

The modern periodic law states that the physical and chemical properties of elements are periodic functions of:

  1. Atomic mass
  2. Atomic radius
  3. Atomic number
  4. Number of neutrons
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Correct answer: C. Atomic number

Modern (Moseley's) periodic law: properties of elements are periodic functions of their **atomic number** ($Z$). This replaced Mendeleev's original law which was based on atomic mass. Why atomic number wins: it explains chemistry better (electronic structure follows $Z$, not mass) and resolves Mendeleev's anomalies (the Ar/K and Te/I pairs whose mass-order disagrees with chemistry-order).

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Elements of the modern periodic table are classified into how many blocks based on the differentiating electron?

  1. 2 (s and p)
  2. 4 (s, p, d, f)
  3. 3 (s, p, d)
  4. 5 (s, p, d, f, g)
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Correct answer: B. 4 (s, p, d, f)

**Four blocks** based on which subshell the differentiating electron enters: - **s-block**: Groups 1 and 2 (Li, Na, K, Be, Mg, Ca, etc.) - **p-block**: Groups 13 to 18 (B, C, N, O, F, halogens, noble gases) - **d-block**: Groups 3 to 12 (transition metals) - **f-block**: Lanthanides and actinides (separated below the main table) No g-block has been confirmed experimentally yet, though it's predicted for superheavy elements ($Z > 120$).

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Across a period from left to right, the atomic radius generally:

  1. Decreases
  2. Remains constant
  3. Increases
  4. First increases then decreases
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Correct answer: A. Decreases

Atomic radius **decreases** from left to right across a period. Why: nuclear charge ($Z$) increases by 1 as you move right, pulling electrons closer. The added electron enters the same shell so screening barely increases — the net effect is stronger attraction and smaller radius. Across period 2: Li (152 pm) → Be → B → C → N → O → F (72 pm). Roughly halves. Down a group, atomic radius *increases* (electrons go into higher principal shells, further from nucleus).

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More Chemistry topics

Ideal and Non-Ideal SolutionsIdeal SolutionsNon-Ideal SolutionsReactions in Aqueous SolutionElectrochemistryElectrochemical SeriesCoordination CompoundsSolutions