1.  1.   Nuclearcharge increases and atomic radii decreasesàincrease electronegativity increases across a period.

2. 2.   The melting points increases as you go down thegroup for the diatomic molecules.  Thisis because the strength of intermolecular forces (this case dispersion forces)increases since the atoms have more electrons as you descend the group.

3. 3.   Electrons in anatom can shield each other from the pull of the nucleus. This effect, calledthe shielding effect, describes the decrease in attraction between an electronand the nucleus in any atom with more than one electron shell. The moreelectron shells there are, the greater the shielding effect experienced by theoutermost electrons.

4.  4.   Electronegativity is defined as the ability ofan atom in a molecule to attract electrons to itself. 

Electronegativity is a relative measure of theattraction that an atom has for a shared pair of electronswhen it is    covalently bonded to another atom.

    D: do not provide enough explanation: electronegativevalue is measured from the covalently bonded to another        atom.