An object of indeterminate size marking a
location in space

Point

Explanation:

An object of indeterminate size which marks a location in space is called a point.

A point in geometry has no dimension unlike a line which is one dimensional. In essence, like other bodies, we cannot specify any of the width, length or height of a point.

Points are usually shown with dots. It has no width, length, breadth and other attributes that specifies it. Angle at a point is taken as 360° which is the same as the angle in a circle.

On the other hand, a line is a connects two or more points and it is one dimensional. They usually have lengths.

Therefore, an object of indeterminate size which marks a location in space is a point.  

Hi; /c

No. an alpha particle is a pair of protons and a pair of neutrons, i.e. a helium