Which element is a solid at stp and a good conductor of electricity?
(1) iodine (3) nickel
(2) mercury (4) sulfur

The correct answer is option 3.

Explanation: There are 3 categories of elements:

1. Metals: These are the elements which are usually solid at room temperature. They are good conductors of heat and electricity. They are easily malleable.

2. Metalloids: They have intermediate properties of metals and non-metals.

3. Non-metals: These are the elements which can be solid, liquid or gases at room temperature. They are poor conductors of heat and electricity. They are easily malleable.

From the given elements above:

Option 1: Iodine is a non-metal but it is solid at STP and is a poor conductor of electricity.

Option 2: Mercury is a metal but is liquid at STP. It is an exception to the metals.

Option 3: Nickel is a metal which is solid at STP and is a good conductor of electricity.

Option 4: Sulfur is a non-metal which is solid at STP and is poor conductor of electricity.

Hence, the correct answer is option 3.