Two questions on visa application form

Hi, I am a US citizen, and my family is traveling to tour Guilin, Xian, and Beijing this summer. Two quick questions: Section 1.11 (US ID Card Number): is this the same as my passport number or is this something different? And, 2.8 and 2.9 (contacts/friends in China): If we are traveling independently and are providing proof of round trip tickets and lodging, would we leave these two sections blank? Thanks.