: Surpose two star has same solar mass and same rotation. One star is a hydrogen rich and metal poor and other is metal rich and hydrogen poor. Which star become a red giant star first?

Th hydrogen poor star. A normal star burns hydrogen atoms first. these stars are called main sequence stars. Once the hydrogen fuel gets to low the nuclear fusion in the core stops and the star will expand as a red giant Ofcourse if the star is big enough helium will start to burn and the star will have a new lease in life. but that is another story. All stars must be made up primaraly by hydrogen.