An atom of an element (X) has its K, L and M shells filled with some electrons. It reacts with sodium metal to form a compound Nax. The number of electrons in the M shell of an atom of element (X) will be

Options

A. 7
B. 8
C. 2
D. 1

Explanation

To determine the number of electrons in the M shell of the element X, we can follow these steps:

### Step 1: Understand the Electron Shell Configuration
Atoms have electron shells labeled as K, L, M, etc. The K shell can hold a maximum of 2 electrons, the L shell can hold a maximum of 8 electrons, and the M shell can hold a maximum of 18 electrons.

### Step 2: Analyze the Reaction with Sodium
The element X reacts with sodium (Na) to form a compound NaX. Sodium has a valency of +1, meaning it loses one electron to achieve a stable electronic configuration. For the compound NaX to be neutral, element X must have a charge of -1.

### Step 3: Determine the Valency of Element X
Since element X has a -1 charge, its valency is 1. This indicates that element X tends to gain one electron to achieve a stable configuration.

### Step 4: Identify the Position of Element X in the Periodic Table
Elements with a valency of 1 and a tendency to gain one electron are typically non-metals found in Group 17 (the halogens) of the periodic table. These elements have 7 electrons in their outermost shell (M shell).

### Step 5: Conclude the Number of Electrons in the M Shell
Since element X is a non-metal with a valency of 1, it will have 7 electrons in its M shell. This is because it needs to gain one electron to complete its octet (8 electrons in the outer shell) for stability.

### Final Answer
The number of electrons in the M shell of an atom of element X is **7**.

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