Answer:
Option C. 52.057
Explanation:
The following data were obtained from the question:
Isotope >> Mass number > Percentage
A (Cr-50) > 50 >>>>>>>>>> 4.3
B (Cr-52) > 52 >>>>>>>>>> 83.8
C (Cr-53) > 53 >>>>>>>>>> 9.5
D (Cr-54) > 54 >>>>>>>>>> 2.4
Average atomic mass =?
The average atomic mass of chromium, Cr can be obtained as follow:
Average atomic mass = [(Mass of A × A%) /100] + [(Mass of B × B%) /100] + [(Mass of C × C%) /100] + [(Mass of D × D%) /100]
Atomic mass of Cr = [50×4.3)/100] + [52×83.8)/100] + [53×9.5)/100] + [54×2.4)/100]
= 2.15 + 43.576 + 5.035 + 1.296
Atomic mass of Cr = 52.057
Therefore, the atomic mass of chromium, Cr is 52.057
Answer: 2. cannot be an element.
Explanation:
Element is a pure substance which is composed of atoms of similar elements.It can not be decomposed into simpler constituents using chemical reactions.Example: Copper 
Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.It can be decomposed into simpler constituents using chemical reactions. Example: methane 

Thus as it can be decomposed into its constituent elements, it is a compound.
Mixture is a substance which has two or more components which do not combine chemically and do not have any fixed ratio in which they are present.
Thus methane cannot be an element.
A generator because they connect each other in physical attraction
Because subatomic particles ARE what make up atoms.
Atoms combine<span> by forming chemical bonds</span>