How many neutrons does element x have if its atomic number is 31 and its mass number is 90?

The two stars in a certain binary star system move in circular orbits. the first star, alpha, has an orbital speed of 36 km/s. the second star, beta, has an orbital speed of 12 km/s. the orbital period is 137 d. a) what is the mass of the star alpha? b) what is the mass of the star beta?

What is the major limitation to the light microscope?

Complete the sentence to describe the law of conservation of energy. the law of conservation of energy states that energy cannot be created