Another JSON query

Here.

A MQL query is either a JSON object, or a JSON array of objects. In fact, the sample object we discussed in previous section about JSON is nearly a valid MQL query. For now, consider the following JSON representation of the chemical element Oxygen:
{
"type": "/chemistry/chemical_element",
"name": "Oxygen",
"symbol": 'O',
"atomic_number": 8,
"ionization_energy": 13.6181,
"melting_point": -2.1835e+2,
"isotopes": []
}

The author has combined query and description. The quotes seem redundant. The empty bracket under isotopes is the event that needs the solution.