1 g of X has atoms arranged in cubic packing so as to give best packing efficiency. The possible arrangement is

Options

A. simple cubic
B. face centred cubic
C. body certred cubic
D. hexagonal close packing

Explanation

To solve the question regarding the arrangement of atoms in cubic packing for the given substance X, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: We need to determine the arrangement of atoms in cubic packing that provides the best packing efficiency for 1 gram of substance X.

2. **Cubic Packing Types**: There are three main types of cubic packing arrangements:
- Simple Cubic (SC)
- Body-Centered Cubic (BCC)
- Face-Centered Cubic (FCC)

3. **Packing Efficiency**: The packing efficiency is the fraction of volume in a crystal structure that is occupied by the atoms. The packing efficiencies for the different cubic arrangements are:
- Simple Cubic: 52%
- Body-Centered Cubic: 68%
- Face-Centered Cubic: 74%

4. **Identifying the Best Packing Efficiency**: From the above efficiencies, we can see that the Face-Centered Cubic (FCC) arrangement has the highest packing efficiency of 74%.

5. **Conclusion**: Since the question specifies that the arrangement should give the best packing efficiency, the possible arrangement for the atoms of substance X is Face-Centered Cubic (FCC).

### Final Answer:
The possible arrangement is Face-Centered Cubic (FCC).

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