You're absolutely right! Both a hydride ion (H⁻) and a helium atom (He) have the same number of electrons: 2.

Here's why:

* Hydride ion (H⁻): A hydrogen atom (H) normally has 1 proton and 1 electron. When it gains an electron, it becomes a hydride ion (H⁻), now having 1 proton and 2 electrons.

* Helium atom (He): A helium atom has 2 protons and 2 electrons.

Therefore, both species have two electrons in their electron shells, making them isoelectronic.