Some elements can have multiple molecular forms in the same physical state. these multiple forms are called
a. isotopes.
b. isotropes.
c. allotropes.
d. multi-tropes.

These are known as allotropes (option c).  A well known example is in the case of Carbon which has diamond, soot, graphite and buckminsterfullerene as solid allotropes. 

Ch4 is nonpolar and insoluble in water. since all of the hydrogen atoms are evenly spread around the carbon atom even through the c h bond is polar all the poles cancel each other out.

Determine the  wavelength of light emitted when an electron  in an li2+ ion  makes a transition from an orbital with n  =  6 to an orbital with n  = 5.