need help with few chemistry questions could anyone help answer or explain, would be helpful.. thanks?

Question

17. Nitrogen atoms each have five valence electrons. How many pairs of electrons must be shared in a molecule of N2?
A. 1
B. 3
C. 4
D. 6

18. A tug-of-war in which neither side is able to move the other side could be used to model a(n) __.
A. covalent bond
B. crystal
C. ionic bond
D. transfer of electrons

19. A white solid is heated in a test tube. The solid slowly changes color to a grayish power, and a gas escapes from the test tube. Is the white solid an element of a compound?
A. t must be an element since it underwent a chemical change
B. It must be an element since it underwent a physical change
C. It must be a compound since it broke down into two new substances
D. Cannot be determined

20. Find the error in the equation and correct it so the equation would be correctly balanced:
Ca(s) + 2H2O(l) --> CaOH2(aq).
A. Ca2(s)
B. H2O(l)
C. Ca(OH)2(aq)
D. both b and c

Answer 1

17. D.
18. A.
19. C.
20. B.

Answer 2

17.
Each nitrogen atom shares three electrons to form a triple bond between the two nitrogen atoms. This leaves one lone pair on each N atom.
Ans B

18.
I don't fully understand your question.
A. Covalent Bonds - electrons are shared.
B. Crystal - ions are held in position by electrostatic attraction.
C. Ionic Bond - One atom loses electrons to become a positive ion. The other atom gains an electrons to become a negative ion. They are then held together by electrostatic attraction.
D. Transfer of electrons - this movement of electrons goes on in ionic bonding - above C.

19.
C. Since it started as white and became grey, a chemical reaction has taken place.Also a gas is liberated. The reaction is 'Thermal Decomposition'. So it is a compound breaking down into two new substances - Ans. C

20.
Ca(s) + 2H2O(l) --> Ca(OH)2(aq) + H2(g)

NB
Calcium = 1 on each side.
Hydrogen = 4 on each side. '2H2' & (--H)2 , H2
Oxygen = 2 on each side '2---O & (O--)2.

Answer 3

B - the question says pairs, not individual electrons.
A
C
#20 makes no sense to me. None of these options seem to balance the equation. While C is a correct response to make the formula for calcium hydroxide correct, none of them actually balance the equation as I see it.

Answer 4

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Answer 5

17. d

18. b

19. a

20. a

i think