Number of Magnetic Substances:

Tinstone:
- Tinstone, also known as cassiterite, is a non-magnetic substance. It is the main ore of tin and has a chemical composition of SnO2.
- Tinstone does not possess any magnetic properties.

Wolframite:
- Wolframite is a magnetic substance. It is a mineral composed of iron, manganese, and tungsten oxide.
- The presence of iron in wolframite contributes to its magnetic properties.

Chromite:
- Chromite is a non-magnetic substance. It is a mineral composed of iron, chromium, and oxygen.
- Despite the presence of iron, chromite does not exhibit any magnetic properties.

Magnetite:
- Magnetite is a highly magnetic substance. It is an iron oxide mineral with a chemical formula of Fe3O4.
- The presence of iron and oxygen in magnetite gives it strong magnetic properties.

Pyrolusite:
- Pyrolusite is a non-magnetic substance. It is a mineral composed of manganese dioxide.
- Despite the presence of manganese, pyrolusite does not possess any magnetic properties.

Rutile:
- Rutile is a non-magnetic substance. It is a mineral composed of titanium dioxide.
- Rutile does not exhibit any magnetic properties.

Magnesite:
- Magnesite is a non-magnetic substance. It is a mineral composed of magnesium carbonate.
- Magnesite does not possess any magnetic properties.

Sphalerite:
- Sphalerite is a non-magnetic substance. It is a mineral composed of zinc sulfide.
- Despite the presence of zinc, sphalerite does not exhibit any magnetic properties.

Summary:
Out of the given substances, the following four are magnetic:
1. Wolframite
2. Magnetite
3. Pyrolusite
4. Sphalerite

The remaining substances, tinstone, chromite, rutile, and magnesite, are non-magnetic in nature.