Which statement explains why NaBr is classified as a compound? 1.
Na and Br are chemically combined in a fixed proportion.
2.
Na and Br are both nonmetals.
3
NaBr is a solid
298 Kand standard pressure.
4.
NaBr dissolves in H20 at 298 K.
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Check the correct box to describe the periodic trends in electronegativity. electronegativity across a period: decreases. increases. electronegativity down a group: decreases. increases.

Which of the following is an example of physical change not a chemical change? a) a log gives off heat and light as it burns. b) a tree stores energy from the sun in its fruit. c) a penny lost in the grass slowly changes color. d) a water pipe freezes and cracks on a cold night.

Select all of the statements which are true. electrons are located in shells or orbits around the atom. electrons orbit slowly around the atom. electrons travel in one flat path around the nucleus of an atom. the valence of an atom is determined by the number of electrons in the atom's outermost shell.