>>Least density-Hydrogen (0.08988kg/m³ at standard condition)
Having the same volume for every mole of gases, hydrogen, which has the lowest molecular mass, is the least dense element, followed by Helium and Neon.
>>Most density-Osmium (22,610kg/m³)
The three noble metals, which exist together both in the periodic table and in nature, also hold the title of the densest material with osmium, iridium, platinum in order. This property is due to the lanthanide contraction.
>>Lowest Melting/Boiling Point-Helium(0.95K, 4.22K)
Helium is a noble gas, having very little attraction between its individual atoms, thus resulting in lowest mp and bp. It is followed by hydrogen and Neon.
>>Highest Melting/Boiling Point-Diamond/Carbon(3800K*/4300K), Rhenium(3459K/5869K*)
Carbon in its diamond form, due to its strong tetrahedral arrangement, has highest mp among all elements, placing over the metals like tungsten, rhenium, osmium, which place second to fourth in order. In terms of boiling point, the order is rhenium, tungsten, osmium, first to third. Because of the high mp and bp of tungsten and the availability in nature, it is used in light bulbs.
>>Highest thermal conductivity-Helium II (>100000W/m.K)
Helium II is liquid helium lower than 2.2K. Because of its high conductivity, it cannot be boiled, but instead directly evaporate into gas. Highest thermal conductivity at normal condition is found in diamond with 2320W/m.K, followed by silver.
>>Highest electrical conductivity-Silver(resistivity=15.87nΩm)
Ignoring superconductors, silver has highest conductivity, or lowest resistivity, followed by two other metals, copper and gold. However, it is notable that silver cannot achieve superconducting state, where resistivity=0. This fact is also employed in real life where almost all wires are made with copper.
>>Most common elements in the universe-Hydrogen
It is predictable since most hydrogen can be easily formed since the start of the universe, while heavier elements are formed by fusion of hydrogen in the stars. It is followed by helium and oxygen.
>>Most stable nucleus-Iron 56
Iron 56 is the most stable nucleus which cannot undergo any nuclear reaction. Any lower mass nucleus can be fused together, while any larger mass nucleus can undergo fission. This follows the fact that if the star has enough fuel, its final form will have iron core, which might lead to neutron star or black hole, without further fusion.
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