The atomic number of an element is 31 and the mass number is 70. The number of electrons in the outer most shell is:

Answer

To determine the number of electrons in the outermost shell of an element with an atomic number of 31 and a mass number of 70, we can follow these steps:

### Step 1: Identify the Element
The atomic number of the element is 31. This corresponds to the element Gallium (Ga) on the periodic table.

### Step 2: Write the Electronic Configuration
The electronic configuration of Gallium (atomic number 31) can be determined as follows:
- The first 18 electrons fill the orbitals up to Argon (Ar):
- 1s² 2s² 2p⁶ 3s² 3p⁶ (which accounts for 18 electrons).
- The remaining 13 electrons will fill the next orbitals:
- 4s² 3d¹⁰ 4p¹.

Thus, the complete electronic configuration for Gallium is:
- **1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p¹**.

### Step 3: Identify the Outermost Shell
The outermost shell for Gallium is the 4th shell, which includes the 4s and 4p orbitals.

### Step 4: Count the Electrons in the Outermost Shell
In the outermost shell (4th shell):
- The 4s orbital has 2 electrons.
- The 4p orbital has 1 electron.

Adding these together:
- Total electrons in the outermost shell = 2 (from 4s) + 1 (from 4p) = **3 electrons**.

### Conclusion
The number of electrons in the outermost shell of the element with atomic number 31 is **3**.

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