Which test should be made before collecting hydrogen in a gas jar?

Explanation

To determine which test should be made before collecting hydrogen in a gas jar, follow these steps:

### Step-by-Step Solution:

1. **Ensure Air is Removed**: Before collecting hydrogen gas, it is essential to ensure that all the air has been removed from the gas jar. This is crucial because the presence of air (specifically oxygen) can affect the properties of hydrogen and its behavior when ignited.

2. **Collect a Sample of the Gas**: Take a small sample of the gas that you believe to be hydrogen in a test tube. This will allow you to perform a test to confirm the absence of air.

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