pOH is defined as the negative base-10 logarithm of the hydroxide ion concentration. This gives pOH = -log10[OH-]. The negative sign is essential because [OH-] in solutions is typically less than 1 M, so log10[OH-] would be negative and pOH would become a positive, convenient value that fits with the pH scale (pH + pOH ≈ 14 at 25°C). Using just log[OH-] would miss that conversion to a positive, intuitive measure. Writing -[OH-] or [OH-] would not reflect a logarithmic measure at all, so they don’t correctly describe pOH.

In beta minus decay, a neutron inside the nucleus is transformed into a proton, with the emission of an electron (the beta particle) and an antineutrino. This conversion increases the number of protons in the nucleus by one, so the atomic number Z goes up by 1. The total number of nucleons stays the same, so the mass number A doesn’t change.

In a single covalent bond, the bonding interaction is a sigma bond formed by end-to-end overlap of atomic orbitals along the line between the two nuclei. This head-to-head overlap concentrates electron density directly between the atoms, creating the strongest, simplest bond that holds them together for a single bond. In contrast, pi bonds arise from sideways overlap of p orbitals and occur in double and triple bonds, adding strength beyond the sigma bond but not forming the single bond itself. Delta bonds involve more exotic, typically d-orbital interactions and aren’t what constitutes a typical single bond. So, the bond type that forms in a single bond is the sigma bond.

Delta H is the overall energy change of the reaction, equal to the difference in energy between products and reactants on a reaction coordinate diagram. On the diagram, reactants sit at one energy level and products at another; delta H = E_products − E_reactants. If delta H is negative, the reaction is exothermic (releases heat); if positive, it’s endothermic (absorbs heat). This is different from the activation energy, which is the energy needed to climb from the reactants up to the transition state (the energy barrier). The energy difference from the transition state to the products is the reverse activation energy. So, the energy difference between reactants and products is the quantity that represents delta H.