The Sun's photosphere is approximately 500 kilometers thick. It is the layer from which most of the sunlight we see escapes, and it is often called the Sun's visible surface even though the Sun has no solid ground.
The photosphere has no sharply defined lower or upper boundary. Instead, solar plasma becomes progressively less opaque with altitude, so the quoted thickness depends on how the layer is defined and measured. Some astronomical references describe it as roughly 100–400 kilometers thick, while educational and popular references commonly round the transition region to about 500 kilometers. Thus 500 kilometers is a fair approximate quiz answer.
Its effective temperature is about 5,772 kelvin, and convection produces bright granules across its surface. Sunspots also appear in the photosphere: they look dark because concentrated magnetic fields inhibit convection, making them cooler than the surrounding material. Above it lie the chromosphere and corona, which are much more tenuous and extend far outward.