(A) is false because [B(H2O)6]3+ does not exist, while [B(OH)4]−is sp3 hybridised and have tetrahedral complex.
The boron atom is electron deficient. It has 6 electrons instead of 8 electrons in its valence shell. Hence, it acts as a Lewis acid by readily accepting the lone pair from oxygen from a2O molecule or OH−ion. Hence, (R) is true.