निम्नलिखित में से वह कौन सा तत्व है जो भूजल को अत्यधिक प्रदूषित और विषैला बनाता है?

Prolonged exposure to extreme cold temperatures may result in tissue damage known as frostbite, which is categorized as a:

In the context of ecosystem energy dynamics, which of the following expressions correctly defines Net Primary Productivity (NPP)?