In analytical chemistry, a trace element or microelement is an element in a sample that has an average concentration of less than 100 parts per million measured in atomic count or less than 100 micrograms per gram. These are those elements essential for plant growth which are needed in only very small (micro). They are: boron (B), copper (Cu), iron (Fe), chloride (Cl), manganese (Mn), molybdenum (Mo) and zinc (Zn).

Correct Option: A

In analytical chemistry, a trace element or microelement is an element in a sample that has an average concentration of less than 100 parts per million measured in atomic count or less than 100 micrograms per gram. These are those elements essential for plant growth which are needed in only very small (micro). They are: boron (B), copper (Cu), iron (Fe), chloride (Cl), manganese (Mn), molybdenum (Mo) and zinc (Zn).

In cement almost entire amount of lime is present in combined state as calcium silicates and calcium aluminates. Cement containing excess amount of lime cracks during setting while cement containing less amount of lime is weak in strength. Setting of cement is an exothermic process.

Correct Option: B

In cement almost entire amount of lime is present in combined state as calcium silicates and calcium aluminates. Cement containing excess amount of lime cracks during setting while cement containing less amount of lime is weak in strength. Setting of cement is an exothermic process.

Dry ice is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue. It is useful for preserving frozen foods, ice cream, etc., where mechanical cooling is unavailable.

Correct Option: D

Dry ice is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue. It is useful for preserving frozen foods, ice cream, etc., where mechanical cooling is unavailable.

Gastric acid is a digestive fluid, formed in the stomach. It has a pH of 1.5 to 3.5 and is composed of hydrochloric acid (HCl) (around 0.5%, or 5000 parts per million), and large quantities of potassium chloride (KCl) and sodium chloride (NaCl). The acid plays a key role in digestion of proteins, by activating digestive enzymes, and making ingested proteins unravel so that digestive enzymes can break down the long chains of amino acids.

Correct Option: C

Gastric acid is a digestive fluid, formed in the stomach. It has a pH of 1.5 to 3.5 and is composed of hydrochloric acid (HCl) (around 0.5%, or 5000 parts per million), and large quantities of potassium chloride (KCl) and sodium chloride (NaCl). The acid plays a key role in digestion of proteins, by activating digestive enzymes, and making ingested proteins unravel so that digestive enzymes can break down the long chains of amino acids.

Geothermal electricity is electricity generated from geothermal energy. Geothermal power is considered to be sustainable because the heat extraction is small compared with the Earth's heat content.

Correct Option: B

Geothermal electricity is electricity generated from geothermal energy. Geothermal power is considered to be sustainable because the heat extraction is small compared with the Earth's heat content.