Periodic Classification of Elements — Important Questions

Decreases gradually

Step 1: Atomic radius is the distance from the nucleus to the outermost electron shell. Step 2: As we move left to right across a period, the shell number (energy level) stays the same. Step 3: However, the atomic number (number of protons) increases from left to right. Step 4: More protons mean a stronger positive nuclear charge that pulls the electrons closer to the nucleus. Step 5: This causes the electron cloud to shrink, so atomic radius decreases across a period from left to right.

Decreases

Step 1: Ionisation energy is the minimum energy needed to remove an electron from a gaseous atom. Step 2: As we go down a group, new electron shells are added, so atomic size increases. Step 3: The valence electrons are now farther from the nucleus and are more loosely held. Step 4: Since the electrons are loosely bound, less energy is needed to remove them. Step 5: Therefore, ionisation energy decreases as we move down a group. This is the opposite of the trend across a period, where ionisation energy increases.

Ore

Step 1: A mineral is any natural compound or mixture of compounds found in the Earth's crust. Step 2: Not all minerals are useful for extraction — only those from which metals can be extracted easily and profitably are called ores. Step 3: For example, both clay and bauxite are minerals of aluminium, but only bauxite is an ore because aluminium can be profitably extracted from it. Step 4: Gangue is the rocky impurity in the ore. Flux is a substance added to remove impurities. Slag is the waste product formed when flux reacts with gangue. Step 5: So the correct answer is Ore.

Hydraulic (Gravity separation) method

Step 1: Different methods of ore concentration are based on different physical properties. Step 2: Hydraulic or Gravity separation works on the principle that ore particles are heavier (more dense) than gangue particles. Step 3: Water is used to wash the crushed ore over a sloping table — lighter gangue washes away while heavier ore settles in grooves. Step 4: Froth floatation uses oil wettability (for sulphide ores). Magnetic separation uses magnetic properties. Leaching uses chemical reagents. Step 5: Haematite (Fe₂O₃), the iron ore, is concentrated by this hydraulic method.