The ratio of `sigma-` bond and `pi-` bond in tetracryano ethylene is `:`

Options

A. `2 :1`
B. `1 :1`
C. `1 : 2`
D. none of these

Explanation

To find the ratio of sigma bonds to pi bonds in tetracyanoethylene, we can follow these steps:

### Step 1: Draw the Structure of Tetracyanoethylene
Tetracyanoethylene has the following structure:
- It consists of a carbon-carbon double bond (C=C).
- Each carbon is bonded to a cyano group (C≡N), which consists of a carbon triple bonded to a nitrogen.

The complete structure can be represented as:
```
N≡C
|
C=C
|
N≡C
```

### Step 2: Count the Sigma Bonds
- Each single bond (C-C or C-N) is a sigma bond.
- Each double bond has 1 sigma bond and 1 pi bond.
- Each triple bond has 1 sigma bond and 2 pi bonds.

In tetracyanoethylene:
- The C=C double bond contributes 1 sigma bond.
- Each C≡N triple bond contributes 1 sigma bond (there are 4 C≡N bonds).

Counting the sigma bonds:
- From the C=C bond: 1 sigma bond
- From the 4 C≡N bonds: 4 sigma bonds

Total sigma bonds = 1 (from C=C) + 4 (from C≡N) = 5 sigma bonds.

### Step 3: Count the Pi Bonds
Now, we count the pi bonds:
- The C=C double bond contributes 1 pi bond.
- Each C≡N triple bond contributes 2 pi bonds.

Counting the pi bonds:
- From the C=C bond: 1 pi bond
- From the 4 C≡N bonds: 4 * 2 = 8 pi bonds

Total pi bonds = 1 (from C=C) + 8 (from C≡N) = 9 pi bonds.

### Step 4: Calculate the Ratio of Sigma to Pi Bonds
Now that we have counted the sigma and pi bonds:
- Sigma bonds = 5
- Pi bonds = 9

The ratio of sigma bonds to pi bonds is:
\[ \text{Ratio} = \frac{\text{Sigma bonds}}{\text{Pi bonds}} = \frac{5}{9} \]

### Final Answer
The ratio of sigma bonds to pi bonds in tetracyanoethylene is **5:9**.

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