Metallurgy, Metals, Non-Metals & Alloy RRB PYQ

Graphite is the only non-metal in this list that is a good conductor of electricity in the solid state because of its unique structure containing delocalized electrons. In graphite, each carbon atom is bonded to only three other carbon atoms in a hexagonal layer, leaving one free valence electron per atom. These free electrons are delocalized and can move freely between the layers of the crystal lattice, allowing the flow of electric current. Although diamond is also made of carbon, all four of its valence electrons are locked in strong covalent bonds, making it an insulator.

Potassium is placed at the top of the reactivity series. It reacts very quickly with water and air, much faster than other metals. This is why potassium is stored under oil to prevent it from reacting with moisture or oxygen in the air. Metals like silver and copper are much lower because they are less reactive.

The reaction where a more reactive metal replaces a less reactive metal from its salt solution is known as a displacement reaction. This process follows the general chemical equation: A + BC → AC + B, where element A is more reactive than element B. It is specifically called a single displacement reaction because only one element is replaced in the compound, distinguishing it from double displacement. Whether a reaction will occur depends on the reactivity series; if the metal added is lower in the series than the metal in the solution, no reaction will take place.

On oxidation, silver changes its colour to black and copper changes its colour to green. Silver oxidizes to form silver sulfide (Ag2S), which appears black. In moist, CO2-rich air, copper oxide further converts to green copper carbonate/hydroxide (verdigris), giving copper its characteristic green patina. Hence, on oxidation, silver turns black and copper turns green.

The only correct statement is only A, which confirms that zinc and lead are more reactive elements than copper. In the activity series of metals, both zinc and lead are positioned above Copper, meaning they can displace copper from its compounds.

Aqua-regia is a highly corrosive mixture of nitric acid and hydrochloric acid in a 1:3 ratio. It is one of the few substances that can dissolve gold and platinum. The name 'aqua-regia' translates to 'royal water' in Latin, due to its ability to dissolve noble metals like gold. It is commonly used in the refining process of gold and in analytical chemistry.

Electrolytic refining is the method used for refining impure metals to obtain them in their purest form. In this setup, a thick block of the impure metal acts as the anode, while a thin strip of pure metal acts as the cathode. When electric current is passed through an electrolyte, the impure metal from the anode dissolves and deposits onto the cathode. The soluble impurities go into the solution, while the insoluble impurities settle down at the bottom of the anode and are known as anode mud.

Gold and Platinum are commonly found in their free, metallic state in nature. These metals are classified as noble metals due to their resistance to corrosion and oxidation in moist air. Gold is often found in nuggets or grains in rocks, in veins, and in alluvial deposits. Platinum can be found in some nickel and copper ores as well as in native deposits. Both metals have been historically significant due to their rarity and economic value.

24-carat gold is referred to as pure gold because it contains 100% gold with no other metal alloys mixed in. Pure 24-carat gold is extremely soft and malleable, making it unsuitable for crafting intricate jewelry as it can easily bend or lose its shape. For making jewelry, gold is typically alloyed with metals like silver, copper, or zinc; the most common standard in India is 22-carat gold, which is 91.6% pure.

Calcium reacts with cold water, but the reaction is less violent than that of sodium or potassium. It forms calcium hydroxide and hydrogen gas: Ca + 2H2O → Ca(OH)2 + H2↑. During the reaction, bubbles of hydrogen gas formed stick to the surface of calcium. As a result, calcium starts floating on the surface of water. Therefore, statement (iii) is correct because calcium reacts less violently with water, and statement (iv) is also correct because hydrogen bubbles adhere to its surface. Thus, statements (iii) and (iv) are correct.