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The triple point of naphthalene is $\pu{-56 °C}, \pu{1.05 kPa}$ (which is much less than $\pu{1 atm}$). So how can a naphthalene ball sublimate at $\pu{1 atm}$, when considering that its melting point at $\pu{1atm}$ is $\pu{78.2 °C}$ (and the boiling point is $\pu{218 °C}$)?

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Naphthalene, as well as any other solid, may sublimate at any temperature and pressure. The triple point parameters are irrelevant. The pressure of other components (that is, air) is irrelevant as well. What is relevant is the vapor pressure of naphthalene itself in the surrounding air, and that is pretty close to $0$. Until it reaches the saturated vapor pressure (or until your mothball is all gone, whatever happens sooner), naphthalene will sublimate.

The solids which we perceive as incapable of sublimation (like steel, glass, or rocks) have very low vapor pressure, so their sublimation would take forever. Other than that, everything above applies to them as well.

Then again, some solids melt upon heating and some do not, but that's another story. We aren't talking about any heating, are we?

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By definition, going from solid to gas directly is sublimation. If moth balls were not solid, but liquid instead, then we'd call the process evaporation.

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    $\begingroup$ This doesn't really answer the question. $\endgroup$
    – bon
    Commented Jan 18, 2017 at 13:26
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    $\begingroup$ Actually it does... $\endgroup$
    – Mithoron
    Commented Jan 18, 2017 at 19:31
  • $\begingroup$ In fact, it is my answer that answers the wrong question. But then again, how was I to know what the OP had in mind? $\endgroup$
    – Ivan Neretin
    Commented Jan 18, 2017 at 19:32
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    $\begingroup$ I really don't see how this is an answer. $\endgroup$
    – orthocresol
    Commented Jan 19, 2017 at 20:53
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I got my answer at wikipedia after a little through study, it goes like this - Evaporation that occurs directly from the solid phase below the melting point, as commonly observed with ice at or below freezing or moth crystals (napthalene or paradichlorobenzene), is called sublimation. So it is actually evaporation but called sublimation
source:https://en.wikipedia.org/wiki/Evaporation

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