diff --git a/src/10_xray.md b/src/10_xray.md
index b55507cc1ced0eb137adff30f577197ee3c94803..0041458dfd9f1b1352aa6fb635559b7f9ee34145 100644
--- a/src/10_xray.md
+++ b/src/10_xray.md
@@ -626,10 +626,11 @@ Bragg's law allows us to obtain atomic distances in the crystal $d_{hkl}$ throug
 ## Exercises
 
 ### Warm up exercises
-1. Why is the amplitude of a scattered wave zero if $\mathbf{k'}-\mathbf{k} \neq \mathbf{G}$?
-2. Calculate the structure factor of the triangular lattice using the reciprocal lattice vectors found in the lecture. 
-Do any intensity peaks dissapear?
-3. Calculate $\mathbf{a}_1 \cdot \mathbf{b}_1$ and $\mathbf{a}_2 \cdot \mathbf{b}_1$ using the definitions of the reciprocal lattice vectors given in the lecture. Is the result what you expected?
+1. Calculate $\mathbf{a}_1 \cdot \mathbf{b}_1$ and $\mathbf{a}_2 \cdot \mathbf{b}_1$ using the definitions of the reciprocal lattice vectors given in the lecture. Is the result what you expected?
+2. Why is the amplitude of a scattered wave zero if $\mathbf{k'}-\mathbf{k} \neq \mathbf{G}$?
+3. Suppose we have a unit cell with a single atom in it. 
+Can any peak intensity peaks dissapear as a result of the structure factor? 
+4. Can the structure factor change when we increase the real-space unit cell?
 
 ### Exercise 1: Equivalence of direct and reciprocal lattice