Correct answer: (c) 4 2 1 3
Explanation
- A
2 3 1 4
2 3 1 4 would make sodium a room-temperature liquid and mercury a poor heat conductor. Sodium is a soft solid; mercury is the liquid metal.
- B
1 4 3 2
1 4 3 2 swaps the knife-cut property onto mercury and makes lead the liquid, which is false.
- C
4 2 1 3
4 2 1 3 matches: sodium can be cut with a knife, mercury is liquid at room temperature, silver is an excellent electrical conductor, and lead is a relatively poor conductor of heat among metals. That is the official key.
- D
4 1 2 3
4 1 2 3 gives mercury the ‘good conductor’ slot and silver the liquid slot. Silver is a solid; mercury is the liquid.
Summary. Official key is (c) 4 2 1 3. Alkali metals are soft; mercury is the familiar liquid metal; silver leads electrical conductivity tables; lead is a dull heat conductor compared with copper or silver. Honour the stored letter (c).