When polonium 210 emits an alpha particle the child isotope has an atomic mass of

The child isotope has an atomic mass of 206.

Explanation:

Isotope are element that have the same number of protons but different number of neutrons i.e they have the same atomic number but different mass number. All isotopes generally have a short half life, which is the time required for individual element to decay to half of its initial size.

An alpha particle has an atomic number of 2 and mass number of 4. So that alpha particle emission by polonium 210 yield a child isotope of lead with atomic mass of 206.

the answer is counterpoint.

counterpoint definition: "the art or technique of playing a melody or melodies in conjunction with another, according to fixed rules."

counterpoint is present in a lot of baroque music- such as bach (notably his wtc prelude and fugues) and scarlatti, but can also be found in music by mozart, beethoven. it can even be found in music as modern as john williams!