What element breaks down into yttrium-90?

The correct answer is Strontium-90.

Strontium-90 breaks down into yttrium-90.

Strontium-90  is a radioactive isotope of strontium. It undergoes β− decay into yttrium-90. A decay energy of 0.546 MeV is also released.

⁹⁰₃₈Sr   -> ⁰₋₁e + ⁹⁰₃₉Yr

Beta particle has the charge and mass of an electron. Upon the release of a beta particle, the mass number of Sr remains unchanged but the atomic number of Sr increases by 1. As a result both Sr and Yt have mass number 90, however, Sr and Yt have atomic numbers 38 and 39 respectively.

a. a primary source combines several different accounts of an event. b. a primary source generally benefits from having been written after an event.

explanation:

8

explanation:

each principal energy level above the first contains one s orbital and three p orbitals. a set of three p orbitals, called the p sublevel, can hold a maximum of six electrons. therefore, the second level can contain a maximum of eight electrons - that is, two in the s orbital and 6 in the three p orbitals.

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