Question

Which of these is a soft heavy metal melts at and used in making a heat sensitive thermometer?
(A) Gallium
(B) Caesium
(C) Sodium
(D) Potassium

Answer 1

Hint :A thermometer with heat-sensitive (thermochromic) liquid crystals in a plastic strip that change colour to show different temperatures is known as a liquid crystal thermometer, temperature strip, or plastic strip thermometer. Liquid crystals have the mechanical characteristics of a liquid yet the visual characteristics of a single crystal.

Complete Step By Step Answer:
Gallium is a chemical element with the atomic number 31 and the symbol Ga. Gallium does not exist as a free element in nature, although it may be found in tiny amounts in zinc ores such as sphalerite and bauxite as gallium (III) compounds. Elemental gallium is a liquid at temperatures over 29.76 °C and will melt in a person's hands at 37.0 °C, the usual human body temperature. Gallium has no recognised biological function. Gallium(III) reacts in biological systems similarly to ferric salts and has been employed in medical applications such as medicines and radiopharmaceuticals. Gallium is a soft silvery metal with a glassy appearance. Its characteristics are similar to those of non-metals in the periodic table, and its metallic qualities aren't as strong as those of most other metals. Gallium in solid form is brittle and has a lower electrical conductivity than lead. Gallium has the second widest liquid range of any element, and is one of the few metals that melts in the palm at ambient temperature (m.pt. 29.76). As a result, it's found in thermometers. Because temperature changes may impact the colour of a liquid crystal, it may be used to monitor temperature.
Hence option A is correct.

Note :
Galinstan is a brand name for a eutectic alloy made up of gallium, indium, and tin that melts at 19 degrees Celsius (2 degrees Fahrenheit) and is therefore liquid at room temperature. Galinstan is also a generic term for a number of related alloys that melt at around +11 °C (52 °F). 68.5 percent Ga, 21.5 percent In, and 10.0 percent Sn makeup Galinstan (by weight). Galinstan has replaced hazardous liquid mercury or the reactive NaK (sodium–potassium alloy) in numerous applications due to the low toxicity and reactivity of its component metals.