1.The Bohr's model is applicable to hydrogenic atoms. It can't be extended even to two electron atoms such as helium. The analysis of atoms with more than one electron was attempted on the lines of Bohr's model for hydrogenic atoms but didn't meet with any success. The fact is that each electron interacts not only with the positively charged nucleus but also with all other electrons.Bohr's model involves electrical force between positively charged nucleus and electron. It doesn't include the electrical force between the electrons which necessarily appear in multi electron atoms