<u>Answer:</u> When oppositely charged species interact.
<u>Explanation:</u>
Ionic compound is defined as the compound which is formed by the complete transfer of electrons from one element to another element.
In these compounds, oppositely charged ions are attracted towards each other to form a compound.
<u>For Example:</u> NaCl is formed by the attraction of 
ions. So, same number of oppositely charges maintain electrical neutrality.
Electrical neutrality in a compound is achieved when atoms forming a compound have same number of opposite charges. Basically the charges on cation is balanced by the charges on anion.
C. inorganic does not contain carbon
Answer: It will take 29 years for a 10.0-gram sample of strontium-90 to decay to 5.00 grams
Explanation:
Radioactive decay process is a type of process in which a less stable nuclei decomposes to a stable nuclei by releasing some radiations or particles like alpha, beta particles or gamma-radiations. The radioactive decay follows first order kinetics.
Half life is the amount of time taken by a radioactive material to decay to half of its original value.
Half life is represented by 
= rate constant
Given : Strontium-90 decreases in mass by one-half every 29 years , that is half life of Strontium-90 is 29 years.
As half life is independent of initial concentration, it will take 29 years for a 10.0-gram sample of strontium-90 to decay to 5.00 grams as the amount gets half.
