Molecular structure and hydrogen bonding of water:
In liquid water, the central oxygen atom has four \(sp^3\) hybrid electron orbitals: two bonded to hydrogen atoms and two occupied by non-bonding lone pairs of electrons.
Through intermolecular hydrogen bonds, each water molecule coordinates with four neighboring water molecules, forming a transient, dynamic tetrahedral network structure.
Ice crystals form a rigid hexagonal lattice, but the fundamental coordination geometry of the water molecule in liquid state is tetrahedral.

Molecular polarity and geometry of water:
Assertion (A) is true: Water (\(\text{H}_2\text{O}\)) is a highly polar molecule with a large permanent dipole moment (\(\mu = 1.85\text{ D}\)).
Reason (R) is true: The water molecule has a non-linear, bent (V-shaped) geometry with an \(\text{H-O-H}\) bond angle of approximately \(104.5^\circ\) due to repulsion between the two lone pairs on the central oxygen atom.
Because of this bent geometry, the individual O-H bond dipole moments do not cancel each other out (unlike in linear \(\text{CO}_2\)); instead, their vector sum produces a significant net molecular dipole moment, making water highly polar. Thus, (R) is the correct explanation of (A).