Chemistry question

d) Polonium is the only metal to occur in the simple cubic arrangement shown below. In the figure below there are eight cubes of length a. Each cube is identical and the structure is repeated millions of times throughout a sample of polonium.
(ii) By considering how a polonium atom in the corner of each cube is shared with a neighbouring cube, state how many polonium atoms are in each cube.
I attached the figure and the mark scheme on the comment. I have no idea what the question is asking for. I don't get what the mark scheme is saying either.
Can someone help me?
Thanks.

What level are you at? e.g. are you going to university in a matter of weeks?

This is the figure and the mark scheme

I am in Y10 rn. GCSE level

Oh wow. Where did you stumble across this?

I was just practising some sixth form chemistry entrance exam.

This is a classic Olympiad or first year undergraduate question.
A single unit cell is just one of the 8 cubes that makes up the figure - not the whole cube.
Look at the single atom in the centre. It is shared between all 8 of the smaller cubes in the figure, which suggests 1/8 of each atom at a vertex of a smaller cube lies within it.
Look at just one of the smaller cubes. How many vertices does it have?
Multiply the number of vertices by the fraction of an atom lying at a vertex (1/8) and that will tell you how many full atoms lie inside each unit cell.

Ok, so that one blue sphere is a single polonium atom?

I am in Y10 rn. GCSE level

Are you doing ur main gcses this year? Or u going in yr 10 in a few days?

Each blue sphere is a single polonium atom, but what fraction of each blue sphere lies in a given smaller cube (notice how the larger cube is divided into 8 equal, smaller cubes?)
The middle sphere (sorry Freudian slip) makes it the easiest to spot

Ok, so that one blue sphere is a single polonium atom? is it 4 vertices per small cube? sorry, i don't quite get it...😅

A cube by definition must have 8 vertices (and 6 faces etc etc) - find a cube and count the number of “corners” it has and count them for yourself.

isn't it 8 spheres per small cube?...😅

That’s how many vertices there are - not how many spheres fit inside each small cube.
If you look closely, you’ll see that not all of each full sphere lies inside a smaller cube. The sphere at the centre makes it easiest to spot as it’s right in the middle of where the 8 cubes meet and so must be split evenly between them. This is why 1/8 of a full atom lies at each vertex.

ohhhhhhh. I finally get it. so the sphere in the middle will be split into 8 small segments. and this will apply to other vertices as well. therefore, 8(vertices) x 1/8(atom segment) = 1

Exactly.
It’s not easy is it - this is why this is usually left to undergraduate level (provided you study chemistry or a closely related field) and isn’t taught at GCSE or A level.