The given number series is: 240, ?, 120, 40, 10, 2.
The task is to find the missing term represented by the question mark.
Let's examine the relationship between the known terms, starting from the end of the series:
The pattern observed is that each term is obtained by dividing the previous term by a decreasing sequence of integers: 5, 4, 3.
To continue this pattern, the divisors should be 2 and then 1.
Now, we calculate the value of $X$ using the first term:
$X = 240 \div 1 = 240$.
Let's verify the complete series with $X = 240$:
The pattern $ \div 1, \div 2, \div 3, \div 4, \div 5 $ holds true.
The missing term in the series is 240.
| List-I | List-II |
| Electronic Configuration | First Ionisation energy (kJ mol$^{-1}$) |
| (A). ns$^2$ | (I). 2100 |
| (B). ns$^2$np$^1$ | (II). 1400 |
| (C). ns$^2$np$^3$ | (III). 800 |
| (D). ns$^2$np$^6$ | (IV). 900 |
| List-I | List-II |
| Spectroscopy | Property |
| (A). Raman | (I). Polarizability |
| (B). FTIR | (II). Dipole Moment |
| (C). UV-Visible | (III). Absorbance |
| (D). NMR | (IV). Spin |