In environmental chemistry, release of which of the following substances into the atmosphere is considered the primary cause of depletion of the stratospheric ozone layer?

Introduction / Context:
The stratospheric ozone layer acts as a protective shield, absorbing much of the Sun's harmful ultraviolet radiation and reducing the risk of skin cancer and other UV related damage. In the late 20th century, scientists discovered that certain man made chemicals were thinning this layer, causing the so called ozone hole. Understanding which substances are primarily responsible for ozone depletion is an important part of environmental chemistry and policy awareness.

Given Data / Assumptions:

• The options include nitrous oxide, hydrogen dioxide, chlorofluro carbon (chlorofluorocarbon, CFC), and carbon monoxide.
• Chlorofluorocarbons are stable compounds used historically in refrigeration, aerosols, and foam blowing.
• We focus on the primary, historically recognised cause of ozone layer depletion.
• We assume typical exam spelling of chlorofluorocarbon as given in the option text.

Concept / Approach:
Chlorofluorocarbons (CFCs) are compounds containing chlorine, fluorine, and carbon. They are chemically inert in the lower atmosphere but eventually diffuse into the stratosphere, where ultraviolet light breaks them down, releasing chlorine atoms. These chlorine atoms participate in catalytic cycles that destroy ozone molecules, converting them into oxygen and thus thinning the ozone layer. Nitrous oxide, carbon monoxide, and water vapour (sometimes loosely called hydrogen dioxide in error) have other environmental impacts but are not considered the primary cause of the ozone hole in standard exam explanations.

Step-by-Step Solution:
Step 1: Recall which gases are historically associated with the ozone hole. CFCs, halons, and related chlorine and bromine containing compounds are known to damage the ozone layer. Step 2: Identify the CFC like option. The option "Chlorofluro carbon" refers to chlorofluorocarbon (CFC). Step 3: Consider other gases in the list. Nitrous oxide is a greenhouse gas and can affect ozone chemistry but is not the primary historical cause taught in textbooks. Carbon monoxide mainly affects local air quality and is not the key ozone depleting substance. Hydrogen dioxide is another name for water, which plays different roles in the atmosphere and is not the main ozone depleting agent.

Verification / Alternative check:
International agreements such as the Montreal Protocol specifically target CFCs and related halogenated compounds because they were identified as the major cause of ozone depletion. Scientific models and observations over Antarctica showed a strong correlation between CFC emissions and ozone layer thinning. While other gases may influence atmospheric chemistry, CFCs and their breakdown products are consistently singled out as the primary culprits in both scientific and textbook accounts. This historical and regulatory focus confirms that chlorofluorocarbons are correctly identified as the main cause.

Why Other Options Are Wrong:
Option A (Nitrous oxide): It is a greenhouse gas and can participate in some ozone related reactions, but it is not the classical primary cause of ozone layer depletion discussed in school level exams. Option B (Hydrogen dioxide): This is essentially water (H2O) and is not responsible for the observed large scale depletion of stratospheric ozone. Option D (Carbon monoxide): CO is a toxic gas affecting local air quality and human health but is not a significant ozone depleting substance in the stratosphere.

Common Pitfalls:
A common mistake is to confuse greenhouse gases that contribute to global warming (such as CO2, CH4, and N2O) with ozone depleting substances. Another confusion arises from the similar sounding names of various atmospheric pollutants. To avoid this, remember that the ozone hole problem led directly to the ban and phase out of CFCs under the Montreal Protocol, making chlorofluorocarbons the key substances blamed for ozone depletion in exam questions.

Final Answer:
The primary reason for depletion of the ozone layer is the release of Chlorofluro carbon (chlorofluorocarbon, CFC) compounds into the atmosphere.