Chemistry

Permanent hardness caused by sulphates of metals cannot be removed by boiling but can be removed by adding lime (calcium hydroxide), which precipitates the sulphates and softens the water.

When an acid reacts with a metal, hydrogen gas is typically liberated due to the metal displacing hydrogen from the acid. This is a common chemical reaction observed with many metals and acids.

Ununoctium, now officially named Oganesson (element 118), is the heaviest man-made element synthesized so far. It is heavier than Promethium, Francium, and Technetium, which are lighter elements.

Sulfuric acid is a strong mineral acid with the chemical formula H2SO4, which consists of two hydrogen atoms, one sulfur atom, and four oxygen atoms.

The chemical formula for zinc hydroxide is Zn(OH)2, which consists of one zinc ion (Zn2+) and two hydroxide ions (OH-). This formula correctly represents the compound's composition.

Carbon has four valence electrons and can form four covalent bonds, giving it a valency of 4.

Diamond is harder than graphite primarily because of its tetrahedral structure, where each carbon atom is strongly bonded to four others in a 3D network, making it extremely hard. Graphite has layers of atoms bonded weakly between layers, which makes it softer.

The molecular formula for glucose is C6H12O6, which represents 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. This is a well-established chemical formula for glucose.

Uranium is the heaviest naturally occurring element found in significant quantities on Earth, with an atomic number of 92. Radium, platinum, and cadmium have lower atomic numbers and are lighter elements.

Lithium is the lightest metal with the lowest density among the given options, making it the correct answer.