Hertsprung russel diagram

How can I think in such a way that I can get a correct answer for this question?
Posted from TSR Mobile

Stars evolve over time. The initial mass of the star will determine it's life cycle, the time over which it evolves and what it's eventual fate is.

So you need to identify from the answers given, which types of star are more likely to be found in a young star cluster (containing young stars that have not lived long yet) vs an old star cluster where many more stars have evolved to old age or have ended up in their final state.

Eliminate each given answer.

For example, are red giants old or young stars?

How do I choose between answer a and b?

Posted from TSR Mobile

How long a star lives depends on how massive it is. A high mass star has more fusion material and because of the higher gravitational forces, the internal pressure will be higher and hence the star will be hotter and use up it's nuclear fuel more quickly than a less massive star.

For example, our sun is a main sequence star of average mass and will live for about 10x10⁹ years.

A more massive star (say 10x that of the sun) may only live for 20x10⁶ years.

So comparing the old star cluster with a new star cluster, we should expect to see less massive stars in the old cluster because most will have already completed their evolution to the final stage.

so you mean the massive star in the old cluster hr diagram has already die so most of them are out of the hr diagram?

will the mass of a star changes as it gets older?

Some have blown up as a supernova and produced remnant nebulae, some will be now be super-giants, some will be white dwarfs, pulsars, etc. When looking at the older star cluster, you will expect to see more of these than compared with the young star cluster. i.e. there will be a higher proportion of star that have left the main sequence in an old cluster and more stars still within the main sequence in a new cluster.

It does, but it is very difficulty to estimate the mass of an individual star or exactly how old that star actually is. Much of astronomy is about comparing observational data with models to make estimates.