What deficiency is this?

[Jt0217]

In fourth week of flower amd some leaves look like this

 

[Steveo123]

That's nitrogen deficiency there buddy! More info and pictures need.
What NPK ratio are you feeding them? How many leaves are like this and where are they located on the plant...etc

 

[twentyeight.threefive]

In fourth week of flower amd some leaves look like this

Looks like you have a potassium deficiency. During flower plants have a higher demand for phosphorus and potassium.