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.

the equation that correctly represent the reaction for formation of ammonia is

n2+ 3h2 → 2nh3 (answer d)

1 mole of nitrogen gas (n2) react with 3 moles of hydrogen gas (h2) to form 2 moles of ammonia ( nh3). this is in a process known as haber process were iron is used as a catalyst and reaction take place that a higher temperature and pressure. the process is exothermic hence energy is released.

answer: c. the experiment shows that the red substance experienced a chemical change.

explanation: chemical change is the change in which chemical composition of the substance changes. physical change is the change in which there is no change in chemical composition.

chemical changes are accompanied by following changes:

a) precipitate formation

b) energy is released or absorbed

c) formation of bubbles

d) change in color

as it is given that the red color has disappeared and there is production of gas, it means the red substance has undergone a chemical change.

e