Which of the following metals cannot be hammered and beaten into thin sheets because it is too soft and reactive?

Introduction / Context:
Malleability is a common property of metals, defined as the ability to be hammered into thin sheets. Many exam questions ask you to identify which metals are malleable and which are not suitable for such treatment. This question focuses on a metal that cannot practically be beaten into sheets because of its physical and chemical properties.

Given Data / Assumptions:

• We are comparing the malleability of gold, silver, potassium, aluminium and copper.
• We assume standard school level knowledge of metal properties.
• The concern is whether the metal can be safely hammered into sheets.

Concept / Approach:
Most metals like gold, silver, aluminium and copper are malleable and can be hammered into thin sheets without breaking. Potassium, however, is an alkali metal that is extremely soft and highly reactive, especially with water and moisture. It can be cut easily with a knife and reacts vigorously with water. Its softness and reactivity make it unsuitable for hammering into sheets in a normal way. Therefore, potassium is the metal that cannot be beaten into sheets in the usual sense tested in school science.

Step-by-Step Solution:
Step 1: Recall that gold is very malleable and can be made into extremely thin gold leaf. Step 2: Remember that silver and copper are also used to make utensils and foils, showing that they are malleable. Step 3: Note that aluminium is used to make aluminium foil, again proving good malleability. Step 4: Recognise that potassium is a very soft, reactive metal that cannot be safely hammered into sheets.

Verification / Alternative check:
You can verify by thinking about common uses. Gold, silver, aluminium and copper are all used in coinage, jewellery or foil, which involves shaping into thin layers. There are no common potassium sheets or foils because the metal reacts quickly with air and moisture and is stored under oil. This strong difference supports potassium as the correct choice.

Why Other Options Are Wrong:
Option A, gold, is one of the most malleable metals known. Option B, silver, is also malleable and used for jewellery and utensils. Option D, aluminium, is widely used as aluminium foil, which clearly shows good malleability. Option E, copper, is used in sheets and wires and is a standard example of a malleable and ductile metal.

Common Pitfalls:
Students may assume that all metals can be beaten into sheets, forgetting that alkali metals like sodium and potassium are exceptions because of their extreme softness and reactivity. To avoid confusion, remember that these metals are stored in oil and are never used in jewellery, utensils or foils. This practical detail signals that they are not handled like common malleable metals.

Final Answer:
The metal that cannot be beaten into thin sheets is Potassium.