Answer:
54
Explanation:
Mass number = protones + neutrons
Mass number = 24 + 30
Mass number = 54
<span>For an atom to have no charge, that is neutral, the number of electrons should be the same to the number of electrons. If the number of electron is more than the number of proton, the atom is negatively charged. Also, when the number of proton is more than the number of electron, the atom is positively charged. The answer to this item is letter C. </span>
Answer:
A
Explanation:
Remember the number of valence electrons represent the group number. As shown in figure, there is only one electron in the valence shell. Therefore, this element belongs to group 1 elements also called as Alkali metals.
Furthermore, the number of electrons in a neutral atom equals number of protons. Hence, there are 11 protons in this element.
Also, number of protons equal atomic number therefore, the atomic number of this element is 11. And, by checking periodic table, the element having atomic number 11 is Sodium (Na).
Hey there!
A half-life means after a certain amount of time, half of that substance will have decayed after that time.
An equation for exponential decay is the following:
y = a(1 - b)ⁿ
Where a is the original amount, b is the rate of decay, and n is time.
1000 is about 0.3 of a half life, 1000 divided by 138 days (3312 hours) is approximately 0.3.
Let's plug in values to that equation:
y = 321(1 - 0.5)^(0.3)
Simplify.
y = 260.73
There will be 260.73mg of polonium-210 remaining after 1000 hours.
Hope this helps!
