JEE Main 2026 — Structure of Atom Question with Solution

Statement A: According to the $(n+l)$ rule, if two orbitals have the same $(n+l)$ value, the orbital with the lower value of $n$ has lower energy. This statement is true.

Statement B: As the atomic number increases, the effective nuclear charge ($Z_{eff}$) increases. The energy of an orbital is proportional to $-\frac{Z_{eff}^2}{n^2}$. Thus, the energy becomes more negative, meaning the energy of the orbitals in the same subshell decreases with an increase in atomic number. This statement is false.

Statement C: The size of an orbital increases with an increase in the principal quantum number $n$. Therefore, the size of the $2p_x$ orbital is less than the size of the $3p_x$ orbital. This statement is true.

Statement D: The number of radial nodes is given by the formula $n-l-1$.
For $5f$: $5-3-1=1$
For $6s$: $6-0-1=5$
For $4d$: $4-2-1=1$
For $5p$: $5-1-1=3$
For $5d$: $5-2-1=2$
Since the $5d$ orbital has exactly $2$ radial nodes, the statement that none of the orbitals have $2$ radial nodes is false.

Therefore, only statements A and C are true.

Answer: A and C only