The number of s-electrons present in an ion with 55 protons in its unipositive state is
The number of s-electrons present in an ion with 55 protons in its unipositive state is
Show Hint
To count s-electrons, include all electrons in the s-subshells up to the element’s configuration.
- 8
- 12
- 9
- 10
The Correct Option is D
Solution and Explanation
The element with 55 protons is cesium (Cs), and its atomic number is Z = 55. The electronic configuration of neutral Cs is:
\(Cs : [Xe] 6s ^1\)
For the unipositive ion Cs+, it loses the single 6s electron, and the configuration becomes:
\(Cs^+: [Xe]\)
Now count the total number of s-electrons in\( Cs^+:\)
• \(1s^2, 2s^2, 3s^2, 4s^2, 5s^2\) contribute \(2 × 5 = 10\) s-electrons.
Thus, the number of s-electrons is 10.
Top Questions on Atomic Models
- Two electrons are moving in orbits of two hydrogen like atoms with speeds $3\times10^{5}\,\text{m/s}$ and $2.5\times10^{5}\,\text{m/s}$ respectively. If the radii of these orbits are nearly same then the possible order of energy states are ___ respectively.
- JEE Main - 2026
- Physics
- Atomic Models
Considering Bohr’s atomic model for hydrogen atom :
(A) the energy of H atom in ground state is same as energy of He+ ion in its first excited state.
(B) the energy of H atom in ground state is same as that for Li++ ion in its second excited state.
(C) the energy of H atom in its ground state is same as that of He+ ion for its ground state.
(D) the energy of He+ ion in its first excited state is same as that for Li++ ion in its ground state.- JEE Main - 2025
- Physics
- Atomic Models
- One mole of an ideal gas expands from 10 dm\(^3\) to 20 dm\(^3\) through an isothermal reversible process. Find \( \Delta U \), \( q \), and \( w \).
- JEE Main - 2025
- Chemistry
- Atomic Models
- Incorrect order of atomic radius is?
- JEE Main - 2025
- Chemistry
- Atomic Models
- Dalton’s Atomic Theory could not explain which of the following?
- NEET (UG) - 2025
- Chemistry
- Atomic Models
Questions Asked in JEE Main exam
Which one of the following graphs accurately represents the plot of partial pressure of CS₂ vs its mole fraction in a mixture of acetone and CS₂ at constant temperature?
- JEE Main - 2026
- Organic Chemistry
- For two identical cells each having emf \(E\) and internal resistance \(r\), the current through an external resistor of \(6\,\Omega\) is the same when the cells are connected in series as well as in parallel. The value of the internal resistance \(r\) is ________ \(\Omega\).
- JEE Main - 2026
- Current electricity
- For three unit vectors \( \vec a, \vec b, \vec c \) satisfying \[ |\vec a-\vec b|^2 + |\vec b-\vec c|^2 + |\vec c-\vec a|^2 = 9 \] and \[ |2\vec a + k\vec b + k\vec c| = 3, \] the positive value of \( k \) is:
- JEE Main - 2026
- Vector Algebra
In the given figure, the blocks $A$, $B$ and $C$ weigh $4\,\text{kg}$, $6\,\text{kg}$ and $8\,\text{kg}$ respectively. The coefficient of sliding friction between any two surfaces is $0.5$. The force $\vec{F}$ required to slide the block $C$ with constant speed is ___ N.
(Given: $g = 10\,\text{m s}^{-2}$)
- JEE Main - 2026
- Rotational Mechanics
- The system of linear equations
$x + y + z = 6$
$2x + 5y + az = 36$
$x + 2y + 3z = b$
has- JEE Main - 2026
- Matrices and Determinants