The word 'ecological' is related to

The word 'ecological' (বাস্তুতান্ত্রিক) is derived from 'ecology' (বাস্তুবিদ্যা), which is the scientific study of the relationships between living organisms (including humans) and their physical environment. It encompasses the interactions among species and between them and their natural surroundings.

Let's analyze the options:

    
•         Environmental (পরিবেশগত): This is the most fitting answer. 'Environmental' refers to everything that surrounds an organism – the natural world, physical conditions, and how they affect life. Since ecology is fundamentally the study of these interactions within the environment, 'ecological' and 'environmental' are very closely related and often used interchangeably in contexts discussing nature and its systems.     
    
•         Atmospheric (বায়ুমণ্ডলীয়): This term specifically relates to the atmosphere, the layer of gases surrounding Earth. While the atmosphere is a crucial component of the environment, 'atmospheric' is too narrow a term to fully encompass the broader meaning of 'ecological', which includes land, water, and living organisms.     
    
•         Biological (জৈবিক): This term pertains to biology, the study of living organisms. Ecology is indeed a branch of biology, but 'biological' focuses more on the life processes and structures of organisms themselves, rather than their interaction with their surroundings, which is the core of 'ecological'.     
    
•         Demographic (জনসংখ্যার): This relates to the characteristics of human populations, such as size, growth, density, distribution, and vital statistics. It has no direct relation to the study of ecosystems or the environment in general.     
    
•         Geographical (ভৌগোলিক): This term relates to geography, the study of the physical features of the earth and its atmosphere, and human activity as it affects and is affected by these. While geographical factors are important for understanding ecological systems, 'environmental' provides a more direct and comprehensive link to the concept of 'ecological' in terms of biotic and abiotic interactions.     

Therefore, 'ecological' is most directly and comprehensively related to 'environmental'.