The increasing order of energy of the orbitals 1s,2s,2p is

 For multi electron system, the energy of orbitals is depend on both Principal quantum number (n) and azimuthal quantum number (l). So, n+l rule is following while electrons are filled up in the orbitals.

$\mathrm{For} 1\mathrm{S}\to \mathrm{n}+\mathrm{l}=1+0=1$

$\mathrm{For} 2\mathrm{S}\to \mathrm{n}+\mathrm{l}=2+0=2$

$\mathrm{For} 2\mathrm{p}\to \mathrm{n}+\mathrm{l}=2+1=3$

Therefore, the increasing order of energy of the orbitals 1s,2s,2p is $1\mathrm{s}<2\mathrm{s}<2\mathrm{p}$.