What is the formula of acrolein?A)C{{H}_{2}}=CH-CN B) C{{H}_{2}}=CH-CHOC) C{{H}_{2}}=CH-COOHD) C{{H}_{2}}=CH-CON{{H}_{2}}

The correct formula of acrolein is **B) C{{H}_{2}}=CH-CHO**.

### Explanation:
Acrolein, also known as **propenal**, is the simplest unsaturated aldehyde. Its chemical structure consists of a carbon-carbon double bond (C=C) followed by an aldehyde group (-CHO). The structure of acrolein can be broken down as follows:

- **C{{H}_{2}}=CH-** represents the vinyl group (a carbon-carbon double bond between two carbon atoms).
- **-CHO** represents the aldehyde group.

Thus, the complete formula is **C{{H}_{2}}=CH-CHO**, which corresponds to option **B**.

### Why the other options are incorrect:
- **A) C{{H}_{2}}=CH-CN**: This is vinyl cyanide, also known as acrylonitrile, not acrolein.
- **C) C{{H}_{2}}=CH-COOH**: This is acrylic acid, not acrolein.
- **D) C{{H}_{2}}=CH-CONH_{2}**: This is acrylamide, not acrolein.

So, the correct answer is **B) C{{H}_{2}}=CH-CHO**.