An isotone of `_(32)Ge^(36)` is
i. `_(32)Ge^(77)` ii. `_(33)As^(77)`
iii. `_(34)Se^(77)` iv. `_(34)Se^(78)`

Options

A. Only (i) and (ii)
B. Only i(i) and (iii)
C. Only (ii) and (iv)
D. (ii),(iii) and (iv)

Explanation

To determine which of the given options are isotones of germanium-76 (represented as `_(32)Ge^(76)`), we need to follow these steps:

### Step 1: Understand the concept of isotones
Isotones are atoms of different elements that have the same number of neutrons but different atomic numbers and mass numbers.

### Step 2: Calculate the number of neutrons in germanium-76
The number of neutrons (N) can be calculated using the formula:
\[ N = A - Z \]
where \( A \) is the mass number and \( Z \) is the atomic number.

For germanium-76:
- Mass number (A) = 76
- Atomic number (Z) = 32

Calculating the number of neutrons:
\[ N = 76 - 32 = 44 \]

### Step 3: Analyze each option to find isotones
Now, we will check each of the given options to see if they have 44 neutrons.

1. **Option i: `_(32)Ge^(77)`**
- Mass number (A) = 77
- Atomic number (Z) = 32
- Neutrons: \( 77 - 32 = 45 \) (Not an isotone)

2. **Option ii: `_(33)As^(77)`**
- Mass number (A) = 77
- Atomic number (Z) = 33
- Neutrons: \( 77 - 33 = 44 \) (Isotone)

3. **Option iii: `_(34)Se^(77)`**
- Mass number (A) = 77
- Atomic number (Z) = 34
- Neutrons: \( 77 - 34 = 43 \) (Not an isotone)

4. **Option iv: `_(34)Se^(78)`**
- Mass number (A) = 78
- Atomic number (Z) = 34
- Neutrons: \( 78 - 34 = 44 \) (Isotone)

### Step 4: Conclusion
The isotones of germanium-76 are:
- Arsenic-77 (`_(33)As^(77)`)
- Selenium-78 (`_(34)Se^(78)`)

Thus, the correct answer is options ii and iv.

### Final Answer:
The isotones of `_(32)Ge^(76)` are:
- ii. `_(33)As^(77)`
- iv. `_(34)Se^(78)`