Metallurgy, Metals, Non-Metals & Alloy RRB PYQ

Mercury is the only metal that is in a liquid state at room temperature. It has a melting point of -38.83 degrees Celsius (-37.89 degrees Fahrenheit), which allows it to remain liquid at room temperature. Mercury is used in various applications, including thermometers, barometers, and fluorescent lamps.

When Magnesium (Mg) ribbon is burnt in air, Magnesium Oxide (MgO) is formed. A bright white light is produced when the ribbon is burnt and powdery ash i.e. MgO is formed. The reaction is a highly exothermic reaction, i.e. a lot of heat is produced. The oxygen in the air reacts with Mg to form MgO: 2Mg + O2 → 2MgO + energy, is the balanced equation for this reaction.

In the activity series, Zinc (Zn) is more reactive than Iron (Fe). Therefore, Zinc can displace Iron from Iron Chloride in a displacement reaction. This reaction can be represented as: Zn(s) + FeCl2(aq) → ZnCl2(aq) + Fe(s). The order of reactivity is known as the reactivity series, in which reactivity decreases from top to bottom: K > Na > Ca > Mg > Al > C > Zn > Fe > Sn > Pb > H > Cu > Ag > Au > Pt.

Potassium is a highly reactive metal and reacts readily with water, forming potassium hydroxide and hydrogen gas: 2K + 2H2O → 2KOH + H2↑. Zinc does not react with cold water; it reacts with steam to form zinc oxide and hydrogen. Aluminium generally does not react with water because its surface is protected by a thin layer of aluminium oxide, though it can react with steam. Lead also does not react with water. Therefore, among the given metals, potassium shows the most immediate reaction with water and is the correct option.

HCl + NaOH → NaCl + H2O is not a displacement reaction but a neutralization reaction. In this reaction, an acid (HCl) reacts with a base (NaOH) to form a salt (NaCl) and water (H2O). Unlike a single displacement reaction where one element replaces another, this involves an exchange of ions between two compounds. A standard displacement reaction occurs when a more reactive element takes the place of a less reactive element within a compound.

The greater the electropositive character of a metal, the greater its tendency to lose electrons and react; similarly, the greater the electronegative character of a non-metal, the greater its tendency to gain electrons and react. Calcium belongs to the family of alkaline earth metals. While going down the second group of the modern periodic table reactivity of the alkaline earth metals goes on increasing. Reactivity of elements: Calcium(Ca) > Magnesium(Mg) > Aluminium(Al) > Zinc(Zn) > Iron(Fe) > Tin(Sn) > Lead(Pb) > Copper(Cu) > Mercury(Hg) > Silver(Ag).

Silver belongs to a group of metals called Noble Metals. Noble metals are less reactive and resist corrosion due to oxygen exposure. This makes them valuable for applications like jewelry and electrical contacts. Zinc (Zn), Aluminium (Al), and Lead (Pb) are all reactive metals and will form oxides when exposed to oxygen, especially at high temperatures.

Zinc will displace the metal from a solution of lead nitrate and silver nitrate. Zinc is more reactive than lead, so it will displace lead from the solution, forming zinc nitrate and lead metal. Aluminium is more reactive than zinc, so aluminium can displace zinc from zinc sulphate solution, forming aluminium sulphate and zinc metal: 2Al + 3ZnSO4 → Al2(SO4)3 + 3Zn.

Zinc will react only with CuSO4 and AgNO3 because zinc is more reactive than copper and silver, allowing it to displace them from their salt solutions: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s); Zn(s) + 2AgNO3(aq) → Zn(NO3)2(aq) + 2Ag(s). In the reactivity series, zinc is placed above copper and silver, but it is below magnesium; therefore it cannot displace magnesium. Zinc cannot react with its own salt solution as there is no difference in chemical potential to trigger a displacement. In the CuSO4 tube, the blue colour will fade and reddish-brown copper will deposit, while in the AgNO3 tube, shiny silver crystals will form on the zinc surface.

Copper is a relatively noble metal; its standard electrode potential is high, so it oxidises far less readily than iron, zinc or magnesium. In moist air, copper quickly develops a thin, adherent patina (basic copper carbonate) that seals the surface and blocks further corrosion. By contrast, iron forms porous rust that flakes off, while magnesium and zinc are much more reactive and corrode faster despite their oxide films.