Hydrazine is a polar compound that possesses the requirements for hydrogen bonding: an "acidic hydrogen" (a hydrogen bonded to a highly electronegative atom such as oxygen, nitrogen or fluorine) and the presence of a lone pair. Both Nitrogen atoms in hydrazine have lone (unshared) electron pairs, and all four hydrogen atoms are "acidic," making hydrazine a candidate for intermolecular hydrogen bonding.

Melting point is inversely related to the strength of intermolecular forces between molecules. In other words, the higher the attractive forces between molecules, the harder they will be to pull apart from a solid into a liquid state during melting. Thus, nonpolar compounds experiencing relatively weak intermolecular forces (dispersion/van der Waals forces) tend to have lower melting points than polar compounds experiencing dipole-dipole or hydrogen bonding interactions, and lower still than ionic compounds with strong attractions between positive and negative ionic species. Thus, in this list, the nonpolar compound  has the lowest melting point, followed by the polar compound  The ionic compound  has the highest melting point.

Start by drawing the Lewis structure of .

Selenium has  fluoride molecules bonded to it, and it has a lone pair. This means its steric number is . A molecule with a steric number of  and  lone pair has a seesaw molecular geometry. Note that this is an expanded octet.

Start by drawing the Lewis structure of .

Notice that the central oxygen atom has  other oxygen atoms bonded to it, as well as a lone pair. This means it has a steric number of . A molecule with a steric number of  and  lone pair has a bent molecular geometry.

Start by determining the steric number of the circled oxygen atom. Since it is bonded to a hydrogen and a carbon and has  lone pairs, its steric number must be . A molecule with a steric number of  and  lone pairs has a bent molecular geometry.

In order to figure out the molecular geometry of the circled element, first determine the steric number.

The circled nitrogen has three electron groups attached to it, so its steric number is . Since there are no lone pairs on the nitrogen, its electron geometry and its molecular geometry are both trigonal planar.

In order to figure out the molecular geometry of the circled element, first determine the steric number.

Since the circled oxygen has four electron groups attached to it, its steric number is . The circled oxygen also has  lone pairs of electrons attached to it; therefore, it has a bent molecular geometry.

In the water molecule, there are four electron groups (steric number is four). Two of them (two pairs) are bonded (the bonds between both hydrogen atoms and the oxygen atom), while the other two are lone pairs on oxygen. Thus, the water molecule has a bent shape, with two bonded electron groups and two lone pair electron groups. A linear VSEPR shape has two electron groups, a trigonal planar has three electron groups, and a trigonal bipyramidal shape has five electron groups.

The Valence Bond theory states that covalent bonds are formed from atomic orbital overlap while the Molecular Orbital theory is the mathematical combination of atomic orbitals to produce anti bonding and bonding orbitals.  

Hybridization occurs through combining atomic orbitals, a concept consistent with Valence Bond theory. Common bonds found in Valence Bond hybridization are sigma and pi bonds which overlap end-to-end or side-to-side respectively. Orbitals are combined in Molecular Orbital theory, producing either bonding or anti bonding orbitals. Molecular Orbital theory shows the destructive or constructive interference of sigma and pi bonds (displayed through bonding and anti bonding orbitals).  

A molecule that has 4 electron groups and 2 lone pairs has an VSEPR notation of:.  The  indicates the central atom, the  the number of bonding atoms, and  the number of lone pairs.  There are 2 bonding atoms and 2 lone pairs, totaling a total of 4 electron groups.  All tetrahedral geometries consist of 4 electron groups. Molecular geometries of electron groups with the tetrahedral are tetrahedral (), trigonal pyramidal (), and bent ().  

Therefore the correct answer is: , tetrahedral, bent.