Which of the following will cause a nail tip to crack?

Trimming a nail tip with a fingernail clipper can lead to cracking because the clipper may not provide an even or smooth cut, particularly if the clipper is not sharp or is used improperly. This uneven edge can create stress points on the nail tip, making it more susceptible to cracking under pressure or impact. Additionally, if the clipper is used too forcefully or at an incorrect angle, it can result in a jagged edge, further compromising the integrity of the nail tip.

The other options can affect the health of the nails, but they do not directly lead to cracking in the same way that improper trimming does. For instance, excessive nail polish might weigh down the nails, but it does not create structural weaknesses that can lead to cracking. Coarse nail files could create rough edges and contribute to general nail damage, but they are more likely to result in splitting or peeling rather than outright cracking. Excessive filing of the natural nail can thin the nails, making them weaker, but again, it does not specifically lead to cracking like improper trimming would.