A. The number of valence electrons increases as atomic mass increases. == Generally true for the representative elements since atomic mass generally increases with increasing Z.
B. The reactivity of alkali metals increases as atomic mass increases. == True. Atomic mass increases down the column and so does reactivity
C. The reactivity of the halogens increases as atomic mass increases. == False. Reactivity decreases down the column.
D. The number of valence electrons decreases across a period. == False. In general, the number of valence electrons increases across a period, particularly for the representative elements.
Pretty sure 1d is not a real thing
Gold is known to be an element. The term that best describes 10-karat gold is that it is an homogeneous mixture.
- Gold as an element of often has an ideal state of purity where there contains nothing but gold atoms.
A heterogeneous mixture is known to be a mixture that cannot be chemically sound everytime. Gold jewelry is known to be a homogeneous mixture as it is always will look good and remain unchanged for a long time.
As good example of homogeneous products, e.g a 1-kilogram 24-karat gold bar has unique properties.
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I guess it would be a psychoactive substance i'm not really sure.. but i hope this helped