Which equation represents a physical change?

(1) H,0 (s) +6.01 kJH,0 (4)

(2) 2H, (g) +0,(g)--2H2O(g) + 483.6kJ

(3) H,(g) +12(g) + 53.0kJ →→ 2HI(g)

(4) N. (g) +20,(g) + 66.4k]— 2NO (9)

Select one:
a. reaction 1 only
b. reactions 1 &3
c. reactions 2&4
d. all reactions