Answer:
The correct answers are first, fourth, fifth
Explanation:
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.
The accepted model of the atom was changed. JJ Thomson discovered the electrons and performed experiment using the cathode ray tube. The model before his did not have electrons so the model was changed. Hope this helps
