Answer: 20.2
Explanation:
Mass of isotope 1 = 20
% abundance of isotope 1 = 90.5% = 
Mass of isotope 2 = 22
% abundance of isotope 2 = 8.0% = 
Mass of isotope 3 = 23
% abundance of isotope 3 = 1.5% = 
Formula used for average atomic mass of an element :
![A=\sum[(20\times 0.905+(22\times 0.08)+(23\times 0.015]](https://tex.z-dn.net/?f=A%3D%5Csum%5B%2820%5Ctimes%200.905%2B%2822%5Ctimes%200.08%29%2B%2823%5Ctimes%200.015%5D)
Therefore, the average atomic mass of the element is 20.2.
To determine the mass of the sample, first find the volume difference after and before the aluminum was placed, the volume change is equal to the volume of the submerged object, in this case aluminum.
Then knowing volume of aluminum and the density of it, we can solve for the mass.
D = m/v
Dv = m
2.7 g/ml • 8 ml = 21.6 grams.
The best and most correct answer among the choices provided by your question is the second choice or letter B.
<span>Regarding the second electron affinity for an oxygen, i. e., the electron affinity for O-, it is much larger and negative.</span>
I hope my answer has come to your help. Thank you for posting your question here in Brainly. We hope to answer more of your questions and inquiries soon. Have a nice day ahead!
The elements in Groups 1A(1) and 7A(17) are all quite reactive.
<h3>Major difference between Groups 1A(1) and 7A(17) : </h3>
Group 7's halogens, which are non-metal elements, become less reactive as you move down the group. In contrast to the alkali metals in Group 1 of the periodic table, this trend is the opposite. The most reactive element in Group 7 is fluorine.
Alkali metals are soft and reactive metals. They react vigorously with water and become more reactive. And other hand halogens are reactive non metals.
- Elements of group 1A are known as alkali metals. Elements of this group are lithium, sodium, potassium, rubidium, cesium.
- Reactivity increase down group 1 but decrease up group 7 this is because group 7 elements react by gaining an electron. As one move down the group, the amount of electron shielding increases, meaning that the electron is less attracted to the nucleus.
To know more about Groups 1A(1) and 7A(17) please click here :
brainly.com/question/13063502
#SPJ4
They have 6 valance electrons.
