The first twenty elements in the periodic table exist in different states of matter at room temperature (25°C or 298 K). Here is a breakdown of the states of matter for each of these elements:

1. Hydrogen (H): Gas
2. Helium (He): Gas
3. Lithium (Li): Solid
4. Beryllium (Be): Solid
5. Boron (B): Solid
6. Carbon (C): Solid
7. Nitrogen (N): Gas
8. Oxygen (O): Gas
9. Fluorine (F): Gas
10. Neon (Ne): Gas
11. Sodium (Na): Solid
12. Magnesium (Mg): Solid
13. Aluminum (Al): Solid
14. Silicon (Si): Solid
15. Phosphorus (P): Solid
16. Sulfur (S): Solid
17. Chlorine (Cl): Gas
18. Argon (Ar): Gas
19. Potassium (K): Solid
20. Calcium (Ca): Solid

As shown above, the first twenty elements include gases (Hydrogen, Helium, Nitrogen, Oxygen, Fluorine, Neon, Chlorine, Argon), solids (Lithium, Beryllium, Boron, Carbon, Sodium, Magnesium, Aluminum, Silicon, Phosphorus, Sulfur, Potassium, Calcium), and one liquid (Mercury is not included in the first twenty elements).
It’s important to note that the state of an element can change with temperature and pressure. The states listed here are specifically for room temperature conditions.