Explanation:

Statement 3 and 4: The five elements niobium, molybdenum, tantalum, tungsten and rhenium are included in the definition of refractory metals. The wider definition of refractory metals includes all elements with a melting point above 2,123 K (1,850 °C), includes a varying number of nine additional elements: titanium, vanadium, chromium, zirconium, hafnium, ruthenium.
Statement 1 and 2: A fusible alloy is a metal alloy capable of being easily fused, i.e. easily meltable, at relatively low temperatures.
Low melting alloys can be divided up into:
Mercury-containing alloys
Only alkali metal-containing alloys
Gallium-containing alloys (but neither alkali metal nor mercury)
Only bismuth, lead, tin, cadmium, zinc, indium and sometimes thallium-containing alloys