Question

Which of the following orbitals are in the increasing order of energy.

• A. $1s,2s,2p,3s$
• B. $4s,3s,3p,4d$
• C. $5p,4d,5d,4f,6s$
• D. $4p,2s,3s,2p$

Answer 1

The correct option is A $1s,2s,2p,3s$

Energy of the orbital $\propto$ Principal Quantum number

Energy of the orbital $\propto$ $(n+l)$ rule

If $(n+l)$ for two orbitals is same then the energy is judged by ${}^{\prime }{n}^{\prime }$. So order using this rule is and according to Aufbau's principle as shown in picture is:

$1s<2s<2p<3s$

Hence, option $A$ is correct.