We report measurements of the branching fractions and direct CP asymmetries of the decays B0→K+π-, B+→K+π0, B+→K0π+, and B0→K0π0, and use these for testing the standard model through an isospin-based sum rule. In addition, we measure the branching fraction and direct CP asymmetry of the decay B+→π+π0 and the branching fraction of the decay B0→π+π-. The data are collected with the belle II detector from e+e- collisions at the (4S) resonance produced by the SuperKEKB asymmetric-energy collider and contain 387×106 bottom-antibottom meson pairs. Signal yields are determined in two-dimensional fits to background-discriminating variables, and range from 500 to 3900 decays, depending on the channel. We obtain -0.03±0.13±0.04 for the sum rule in agreement with the standard model expectation of zero and with a precision comparable to the best existing determinations.
