chemistry help plz!!!!!!!!!!!?

which pair of elements is listed in order of decreasing first ionization energy?

a) Na, Mg

B) Mg, Al

C) Al, Si

D) Si, P (D is the correct answer)

An element with a low melting point that does not conduct electricity would most likely b found on the periodic table...

a) in the upper right portion (A is the correct answer)

B) in the upper left portion

C) in the lower left portion

D) in the middle

the first thre ionization energies of an element X are 590, 1145, 4912 kj/mol. the most likely formula for a stbale ion of X is

A) X+

B) X2+ (the answer is B huge jump from 2nd ionization energy to 3rd energy)

C) X3+

D) X-

which have both ionic and covalent bonds?

Salts

I. NH4Br

II NaNO2

A) I only

B) II only

C) both (Correct answer is C)

D) neither I or II

How many valence electrons are present in the tetra borate ion (B4O7)^2-

a) 42

B) 54

C) 56 (C is the correct answer, 4 B = 4 x 3; 7 O = 7 x 6; 2 electrons from charge = 56 ve)

D) 62

Which substance has the highest melting point?

a) silicon Carbide (SiC)

B) phosphorus pentachloride (PCl5)

sulfer (S8) I think sulfur but not sure about this one!

phosgene (COCl2)

The above is correct in all reagards except for the last question:

Silicon carbide has the highest mp. The reason is because it is ionic Si(4+)C(4-). S8 is covalent is the bonds are less strong. This reasoning also applies to phosgene, and PCl5.