Answer:
42 19 K→42 20 Ca+e−
Explanation:
Naturally-occurring potassium atoms have a weighted average atomic mass of 39.10 (as seen on most modern versions of the periodic table.) Each potassium atom contains 19 protons p+ and thus an average potassium atom contains about 39.10−19≈20 neutrons n0.
This particular isotope of potassium-42 contains 42 nucleons (i.e., protons and neutrons, combined;) Like other isotopes of potassium 19 out of these nucleons are protons; the rest 42−19=23 are therefore neutrons.
D I have a good feeling about d
Answer:
Ice is a solid form of liquid. Water simply expands when it freezes.
The same amount of water for each shape of ice because the melting rate of ice depends on the surface area of each shape. So the same amount of water or volume with a large surface area will remain frozen for longer time.
Answer:
d.
Explanation:
proposed the ring structure for benezene
Answer: Hydrogen ion concentration of the lake is 
Explanation:
pH or pOH is the measure of acidity or alkalinity of a solution.
pH is calculated by taking negative logarithm of hydrogen ion concentration. Acids have pH ranging from 1 to 6.9 and bases have pH ranging from 7.1 to 14.
To calculate the pH of the solution, we use the equation:
![pH=-\log[H^+]](https://tex.z-dn.net/?f=pH%3D-%5Clog%5BH%5E%2B%5D)
We are given:
pH = 4.0
Putting values in above equation, we get:
![4.0=-\log[H^+]](https://tex.z-dn.net/?f=4.0%3D-%5Clog%5BH%5E%2B%5D)
![[H^+]=10^{-4.0}](https://tex.z-dn.net/?f=%5BH%5E%2B%5D%3D10%5E%7B-4.0%7D)
![[H^+]=10^{-4}](https://tex.z-dn.net/?f=%5BH%5E%2B%5D%3D10%5E%7B-4%7D)
Thus hydrogen ion concentration of the lake is
