1 is D 2 is c 3 is A and 4 the nucleus is so big because it is one of our largest cells in our body... hope this helps!!!!!!!!!!!
Answer : The dipole-dipole interaction.
Explanation : The kind of bond that is created by a weak electrical attraction between two polar molecules is dipole-dipole interaction.
The type of force which occurs between the positive end of one molecule and the negative end of another molecule: is dipole-dipole interaction.
For better understanding, please refer the attachment.
It is important for the pH of blood to remain constant because your blood would ionize and burn up if the pH wasn't constant. And if the pH was too high, bacteria ( good and bad, and foreign) would end up dying, as well as yourself.
Half-life is the time taken for the concentration of the substance to reduce by 50%. The original sample of strontium had a mass of 1.6 gms. Thus, option d is correct.
<h3>What is half-life?</h3>
The half-life of any radioactive substance is the time period at which the concentration will get reduced to half the initial amount. The initial mass of Sr-90 is calculated as,

Given,
Quantity of the remaining substance N (t) = 0.40 gm
Initial radioactive substance quantity
=?
Time duration (t) = 56 years
Half-life = 28 years
Substituting values above:

= 1.6 gm
Therefore, option d. the initial mass of Sr is 1.6 gm.
Learn more about half-life here:
brainly.com/question/16145921
#SPJ4