In Mandarin Chinese, measure words are essential for counting nouns. The correct measure word for 'pencil' is 支 (zhī). Therefore, to say 'one pencil,' you would say 一支铅笔 (yī zhī qiānbǐ). Understanding and using measure words correctly will significantly improve your fluency and accuracy in Mandarin Chinese. Practice using 支 (zhī) with other similar objects to reinforce your learning.