U Question 13
1
Which best explains how photosynthesis is helpful to humans?
It reduces teh amount of harmful rays released by the sun.
It increases the levels of carbon dioxide in the air.
It provides oxygen for humans to breathe.
It produces proteins, which humans can eat.
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What semimetal can form four single covalent bonds.

1)each group 16 element has how many valence electrons? ( )4 ( )6 ( )8 ( )16 2)how many dots appear in the dot structure for calcium ion, ca2+? ( )zero ( )one ( )two ( )eight 3) which of the following atoms forms a cation to obtain an octet of outer shell electrons? ( )magnesium ( )oxygen ( )fluorine ( )helium 4) an al3+ ion contains 13 protons and 10 electrons. ( )true ( )false 5) valence and non-valence electrons are represented in lewis dot structures. ( )true ( )false

Which of the following electromagnetic waves can create ions?