Hi, I was confused about this question, so I submitted it, and it said the correct answer was tellurium. Could you explain why? I'm a bit confused.

It is based on the concept of strength of acids and bases (NON-OXO) down the group.
A hydrogen bonded to an atom is more acidic due to two reasons:

1)More electronegative atom pulls  electron density from hydrogen and releases it as a proton(H+).

2) Big sized atoms make longer bonds with hydrogen which are weaker and easy to break. So these hydrogens are also more acidic because they come out easily as proton(H+) .

In this question atoms have same electronegativity so we will compare the sizes.

Smallest atom will make smallest bond and strongest bond. It will be difficult to break bond of hydrogen with the atom so it becomes weakest acid.

Size order is - down the group size increase because new shells are added.

O < S < Se < Te

Ohhh! So basically, a Bronsted acid releases a hydrogen ion! Oh, and then that also means we are looking at the strongest bonds because of the difficulty in breaking the bond with hydrogen. Okayy. Makes sense, thank you!

wait a second, i am still confused. What about Po? Polorium  is the biggest in size, so isn't that the weakest?

because as you go down the group size increases? So that would mean Po would be the biggest in size and be the weakest Bronsted acid?

As we move down the group size increases and acidity also increases because it is easy to break the bond of H .Big bonds are weak bonds.Hence H₂Po is stronger than H₂Te.
However we know that Po is a rare and radioactive element.

I'm still confused, slightly