Question

ammonia is soluble in water while phosphine is not

Answer 1

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When ammonia is passed through water :
The Ammonia molecule has the capability to form a dative bond due to the lone pair of electrons.There is the formation of a H-bond due to the strong dipole-dipole attraction the ammonia dissolves in water.

When phosphine is passed in water('slightly' soluble):
the lone pair on phosphorus may be regarded as predominantly formed by the 3s orbital of phosphorus. Therefore,it forms weak hydrogen bonds.Thus, the H-Bond is weak and it is only slightly soluble.Phosphine dissolves more readily in non-polar solvents than in water because of the non-polar P-H bonds but water is polar in nature.

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Answer 2

Answer and Explanation:

Hydrogen bonding (H-bonding) is an intermolecular force having partial ionic-covalent character. H-bonding takes place between a hydrogen atom (attached with an electronegative atom e.g. O, N and F) and an electronegative atom (O,N and F).

In $NH_3$, N is a highly electronegative atom attached to a H atom through a covalent bond. Therefore N atom gets partial negative charge and H atoms get partial positive charge.  

As we know like dissolves like. Ammonia becomes polar and is soluble in polar solvent water.

As phosphorous is less electronegative than nitrogen ,thus is not as polar as ammonia and is slightly soluble in polar solvent water.