You need to interrogate the alkane MELTING points...........as a physical scientist you need to interpret data NOT to estimate it.
And of course, you need to examine the actual data. From the table, hexadecane,
You need a graph of alkane melting points.
It should look something like this:
You might define 20 °C as room temperature.
Then you would check the melting points of the alkanes from one carbon up.
The dividing line appears to come between hexadecane (16 carbons, melting point 18 °C) and heptadecane (17 carbons, melting point 21 °C).
Then, heptadecane would the first alkane to be a solid at room temperature.