Which of the following element is not phytotoxic?

Boron element is not phytotoxic.
Phytotoxins are substances that are poisonous or toxic to the growth of plants.
Boron element is not phytotoxic, it plays a key role in a diverse range of plant functions including cell wall formation and stability, maintenance of structural and functional integrity of biological membranes, movement of sugar or energy into growing parts of plants, and pollination and seed set.