Which of the following statements is/are correct?

1. Mercury is the only metal that exists as liquid at room temperature.

2. Among non-metals, carbon has the highest melting point.

3. Hydrogen is the most abundant element in the universe.

4. Oxygen is the most abundant element in the Earth's crust.

A covalent molecule '$$X Y^{\prime}$$' is found to have a dipole moment of $$1.5 \times 10^{-29} \mathrm{C} \cdot \mathrm{m}$$ and $$a$$ bond length of $$150 ~\mathrm{pm}$$. The percent ionic character of the bond will be

The hybridisation of $$\mathrm{Se}$$ in $$\mathrm{SeF}_4$$ and its geometry respectively are :

Incorrect matching amongst the following is (according to geometry of molecules)