Final answer:
The element that is isoelectronic with helium is hydrogen.
Step-by-step explanation:
The correct option is B. H.
Isoelectronic means having the same number of electrons. Helium has 2 electrons. Hydrogen also has 1 electron. Therefore, hydrogen is isoelectronic with helium because they both have the same number of electrons.
Option H is also hydrogen but in its positive ion state, which means it has lost an electron. Therefore, it is not isoelectronic with helium.