Mortar is a workable paste made by mixing cement, sand, and water. It is primarily used in masonry construction to bind bricks, stones, or concrete blocks together. Unlike concrete, which includes coarse aggregates like gravel, mortar is designed to provide a smooth, adhesive bond between building units.

Portland cement is manufactured by heating a finely ground mixture of limestone (calcium carbonate) and clay (which provides silica, alumina, and iron oxide) in a rotary kiln at high temperatures to form clinker, which is then ground into a fine powder.

While the question identifies 'Hard glass' as the answer, in standard chemical literature, Flint glass is typically preferred for optical instruments due to its high refractive index and dispersion properties. This entry is marked with a conflict flag as the provided answer key contradicts standard optical material science.

RDX (Research Department Explosive), also known as cyclonite or hexogen, was first synthesized by Georg Friedrich Henning in 1898. He obtained a German patent for the substance, which was later developed into a powerful military explosive. It is characterized by its high stability and explosive velocity, making it a critical component in modern munitions and demolition charges.

Silicosis is a well-documented occupational lung disease caused by the inhalation of crystalline silica dust, which is abundant in ceramic and glass industries. While the provided answer suggests kidney stones, medical literature strongly links these industries to silicosis. The source answer may be factually incorrect regarding the primary occupational hazard, as kidney stone formation is not typically classified as the primary industrial hazard for these specific sectors.

Limestone (calcium carbonate) is the principal ingredient in cement production. It is heated in a kiln with other materials like clay to form clinker, which is then ground into a fine powder. Gypsum is added later to regulate the setting time of the cement.

Soda-lime glass, which is composed primarily of sodium silicate and calcium silicate, is commonly referred to as soft glass. It is the most prevalent type of glass used in windows and containers due to its relatively low melting point.

Pyrex is a borosilicate glass containing silica and boron trioxide. A key characteristic of borosilicate glass is its very low coefficient of thermal expansion, which makes it highly resistant to thermal shock, unlike standard soda-lime glass. Therefore, statement 2 is incorrect, while 1 and 3 are accurate.

Portland cement is primarily composed of calcium silicates, which are formed by heating limestone (calcium carbonate) and clay (which provides silica, SiO2) in a kiln. Silica (SiO2) is a fundamental building block in the formation of dicalcium silicate and tricalcium silicate, the phases responsible for the hardening and structural strength of cement upon hydration.

Glass wool is a thermal and acoustic insulating material. It possesses high tensile strength relative to its weight, is fire-resistant, and is used in the production of fiber glass. However, it is an electrical insulator and is generally designed to be moisture-resistant, not moisture-absorbent.