Is it a government rule that nobody can fail in class 11th?

No such rule is there as such. Eligibility for Compartment Examination in class 11 and 12 A candidate failing in one of the five subjects of external examination shall be placed in compartment in that subject provided she qualifies in all the subjects of internal assessment. Compartment Examination

Dear Poli, There is no such rule. So, do well in your studies and get good grades. All the best.