* Calcium is a silvery-white metal that is malleable and ductile. It is reactive and tarnishes in air. Calcium is found in many foods, including milk, cheese, and yogurt. It is also used in various products, such as cement, plaster, and fertilizer.
* Gold is a yellow metal that is very dense and malleable. It is resistant to corrosion and tarnishing. Gold is found in nature as nuggets or veins and is used to make jewelry, coins, and other objects.
* Iron is a silvery-gray metal that is very strong and magnetic. It is found in nature as iron ore and is used to make steel, which is used in various products, such as cars, buildings, and appliances.
* Sodium is a soft, silvery-white metal that is very reactive and tarnishes in air. It is found in nature as sodium chloride (common salt) and is used in various products, such as food, soap, and paper.
Here is a table summarizing some of the key properties of calcium, gold, iron, and sodium:
| Property | Calcium | Gold | Iron | Sodium |
|---|---|---|---|---|
| Atomic number | 20 | 79 | 26 | 11 |
| Atomic mass | 40.08 | 196.97 | 55.85 | 22.99 |
| Density (g/cm³) | 1.55 | 19.3 | 7.87 | 0.97 |
| Melting point (°C) | 839 | 1,064 | 1,538 | 97.6 |
| Boiling point (°C) | 1,484 | 2,947 | 3,095 | 892 |
| Reactivity | Reacts with water | Resistant to corrosion | Rusts in air | Reacts with water |
| Uses | Cement, plaster, fertilizer | Jewelry, coins, art | Steel, cars, buildings | Food, soap, paper |
