Please check them,Thanks

[Anonymous]

Order/Advice.
1)Alex: Are there any principles of effective study?
Malleson: Yes, and you ________ learn them.

Order.
Malleson: Yes, and you must learn them.
Malleson: Yes, and you have to learn them.
Advice.
Malleson: Yes, and you ought to learn them.
Malleson: Yes, and you should learn them.

2)Alex: I think I'll study for twenty hours tomorrow
Malleson: You _________ because you'll be too tired to remember anything.
Order.
Malleson: You must not because you'll be too tired to remember anything
Malleson: You have not because you'll be too tired to remember anything
Advice.
Malleson: You should not because you'll be too tired to remember anything
Malleson: You ought not because you'll be too tired to remember anything

3) Alex: I sometimes get fatigued, but I ignore it.
Malleson: Then you __________you'll lose your powers of concentration.
Order.
Malleson: Then you must stop as you'll lose your powers of concentration.
Malleson: Then you have to stop otherwise you'll lose your powers of concentration.
Advice.
Malleson: Then you should stop as you'll lose your powers of concentration.
Malleson: Then you ought to stop otherwise you'll lose your powers of concentration.

4) Alex: I was going to play ping pong after studing, but I don't think I'll bother.
Malleson: But you ________________ A change of activity is essential.
Order.
Malleson: But you have got to play, A change of activity is essential.
Malleson: But you must play A change of activity is essential.

Advice.
Malleson: But you should play A change of activity is essential.
Malleson: But you ought to play A change of activity is essential.

[Francois]

Here's my go:

1. should
2. should not
3. must/should
4. should

FRC

[MikeNewYork]

Order/Advice.
1)Alex: Are there any principles of effective study?
Malleson: Yes, and you ________ learn them.

Order.
Malleson: Yes, and you must learn them.
Malleson: Yes, and you have to learn them.
Advice.
Malleson: Yes, and you ought to learn them.
Malleson: Yes, and you should learn them.

All four are OK.

2)Alex: I think I'll study for twenty hours tomorrow
Malleson: You _________ because you'll be too tired to remember anything.
Order.
Malleson: You must not because you'll be too tired to remember anything
Malleson: You have not because you'll be too tired to remember anything
Advice.
Malleson: You should not because you'll be too tired to remember anything
Malleson: You ought not because you'll be too tired to remember anything

1 and 3 are fine. 2 is incorrect. 4 is OK, but it would be more common in British English than in American English.

3) Alex: I sometimes get fatigued, but I ignore it.
Malleson: Then you __________you'll lose your powers of concentration.
Order.
Malleson: Then you must stop as you'll lose your powers of concentration.
Malleson: Then you have to stop otherwise you'll lose your powers of concentration.

1. I would use "or" instead of "as".
2. This needs a semicolon or a period after "stop".

The first would be a mild order or strong advice.
The second would be advice.

Advice.
Malleson: Then you should stop as you'll lose your powers of concentration.
Malleson: Then you ought to stop otherwise you'll lose your powers of concentration.

Same corrections as above.

Both are advice.

4) Alex: I was going to play ping pong after studing, but I don't think I'll bother.
Malleson: But you ________________ A change of activity is essential.
Order.
Malleson: But you have got to play, A change of activity is essential.
Malleson: But you must play A change of activity is essential.

1. It could also be "have to play". Put a period after "play".
2. Place a period after "play".

I wouldn't call either an order, in context. I would call it more "urging".

Advice.
Malleson: But you should play A change of activity is essential.
Malleson: But you ought to play A change of activity is essential.

Same periods.

Both would be advice.