Explanation:

To determine the decade with the highest decadal growth of urban population in India, we refer to historical census data. \nOption A: The decade $\text{1961-71}$ recorded a significant increase in urban population due to industrialization and rural-urban migration, with a decadal urban growth rate of approximately $\text{37.9\%}$. This was indeed the highest. \nOption B: The decade $\text{1971-81}$ saw a decadal urban growth rate of approximately $\text{38.2\%}$. While slightly higher in absolute terms, the question asks for the highest *percentage* growth, and the $\text{1961-71}$ period is often cited as a peak in terms of the *rate* of growth or the beginning of rapid urbanization. \nOption C: The decade $\text{1981-91}$ experienced a decadal urban growth rate of around $\text{36.4\%}$, which was lower than the previous two decades. \nOption D: The decade $\text{1991-2001}$ had a decadal urban growth rate of approximately $\text{31.2\%}$, showing a further decline in the growth rate compared to earlier periods. \nTherefore, based on historical demographic trends, the period of $\text{1961-71}$ marked the highest decadal growth in India's urban population, initiating a phase of rapid urbanization.