Can this tap be fixed onto a one tap hole basin or does it have to go on the countertop

It is suitable for single hole installation (no matter the hole is on the counter or on the basin), and the required installation hole size is 1.26\"-1.49\" / 32-38mm (1.38\" / 35mm is recommended if to drill the hole).But please kindly refer to the specification to see if the tap size (i.e spout height) is suitable for your basin.