According to ncert strptococus pnemonea is correct, but diplococus and streptococcus pnemonea both are correct because pnemonea causative orgasm first named as diplococus pnemonea(1920) (diplococus -sperical two celled structure)that means it exhibit two cells structure and it also looks like a some chain like structures that's why after it is named as strptococus pnemonea(in 1974).

According to the latest classification, the correct causal agent for pneumonia is Streptococcus pneumoniae. However, in the past, it was commonly referred to as Diplococcus pneumoniae. Both terms are used to describe the same bacterium, but the scientific community now recognizes it as Streptococcus pneumoniae. Let's delve into the details below:

**Pneumonia and Its Causal Agent**
Pneumonia is a respiratory infection that primarily affects the lungs. It can be caused by various agents such as bacteria, viruses, fungi, or even certain chemicals. Among the bacterial causes, Streptococcus pneumoniae is the most common pathogen responsible for pneumonia.

**Historical Terminology**
In the past, the bacterium Streptococcus pneumoniae was often referred to as Diplococcus pneumoniae. This naming convention was based on its characteristic appearance under the microscope. The bacterium typically appears as pairs of cocci (spherical bacteria), resembling two adjacent kidney beans. Hence, they were referred to as "diplococci."

**Updated Classification**
However, with advancements in microbiology, including genetic and molecular analysis, the classification and nomenclature of microorganisms have evolved. The scientific community now recognizes Streptococcus pneumoniae as the correct designation for the bacterium causing pneumonia. This change in terminology reflects a more accurate understanding of the bacterium's genetic makeup, pathogenesis, and phylogeny.

**Importance of Correct Classification**
Using the correct scientific name, Streptococcus pneumoniae, helps to ensure that there is no confusion or ambiguity when discussing the bacterium and its role in causing pneumonia. It allows for accurate communication among healthcare professionals, researchers, and scientists, leading to effective diagnosis, treatment, and prevention strategies.

**Conclusion**
In summary, the causal agent for pneumonia is Streptococcus pneumoniae. Although it was historically referred to as Diplococcus pneumoniae, the scientific community now recognizes the correct nomenclature as Streptococcus pneumoniae. Using the updated classification system ensures accurate communication and understanding of the bacterium's role in causing pneumonia.