What will be the atomic number of the last member of the seventh period in the long form of the periodic table?

Options

A. 116
B. 118
C. 120
D. 122

Answer

To find the atomic number of the last member of the seventh period in the long form of the periodic table, we can follow these steps:

### Step 1: Understand the structure of the periodic table
The periodic table is organized into periods (horizontal rows) and groups (vertical columns). The seventh period is the last row of the periodic table.

### Step 2: Identify the last group of the seventh period
The last group in the seventh period corresponds to the noble gases, which are located in Group 18. The noble gases in the periodic table include helium, neon, argon, krypton, xenon, and radon.

### Step 3: Determine the atomic number of radon
Radon is the last element in the sixth period and has an atomic number of 86.

### Step 4: Calculate the atomic number of the last member of the seventh period
To find the atomic number of the last member of the seventh period, we need to add 32 to the atomic number of radon (86). This is because the transition from the sixth to the seventh period involves adding 32 to the atomic number.

\[ \text{Atomic number of last member of 7th period} = \text{Atomic number of Radon} + 32 = 86 + 32 = 118 \]

### Conclusion
The atomic number of the last member of the seventh period in the long form of the periodic table is **118**.

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